Unfortunately, it seems to be the rule that practice rarely lives up to the ideal, and not just in politics or philosophy. That being said, I still think that Marx and Engels rank among the great world changing scientists produced in the advance capitalist countries in the 19th century. I also believe that fundamental insights of Marxism remain as true today as when they wrote the Communist Manifesto  and Origins of the Family, Private Property and the State. 
Among these fundamental thesis as I understand them are these, and I am expressing this simply:
Technological development has enabled economic development which in turn has powered social and political development. The way this has worked out in the broad sweeping arch of human history is pretty much the way it had to work out. Basically, we had to do through a lot of bad stuff to be able to get to a better place and we aren't there yet. To wit:
After millions of years of evolution, the modern human species evolved from the primates, and after several hundred thousand years we began exploring shores beyond Africa until after several epic migrations, we had established human communities in just about every corner of the Earth that could be gotten to on foot or in simple boats.
These early human societies practiced a kind of primitive communism. They had yet to divide into classes and they had no state as we know it now, i.e. a body exercising a monopoly of violence. They lived like indigenous Americans lived in this country before the white man came to it. The land was not considered private property and most things were shared communally. Important decisions were made by the community as a whole or by tribal elders who held no power or authority not freely granted to them by the respect of the community. This is how all nations began, although some, like those in the Tigris and Euphrates river valley had already moved beyond that stage some 8,000 years ago while the native Americans were still stumbling through it when the European imperialists showed up with horses about 500 years ago, and a few aboriginal people are still at that stage even today.
While some in the more advanced cultures have tried to use these different rates of development as proof of some sort or racial supremacy, I believe they are due almost entirely to geography. When viewed in the context of the entire scope of human history, these difference are as between two children that may learn to walk or talk at ages a few weeks difference.
The problem with primitive communism was never the communism part. It was the primitive part. Little food, poor medicines, poor housing, being cold or hot all the time, dying very young, and of course, no Internet. So humanity's quest to better itself led to technological development. We developed agricultural and animal husbandry; those allowed us to built stable communities that could stop wandering and get established in one place. The domestication of animals also created the first important form of private property and portable wealth. This began the age of the haves and have nots, this laid the basis for the first class societies, the slave societies that dominated ancient civilizations everywhere.
Prior to these technological developments, slavery was impossible. Slavery as a system requires that the slave be at least productive enough to sustain herself and still produce some excess that can be appropriated by her master. The use of the feminine pronoun is most appropriate here. After domesticated animals got established as private property, the path was open to view other human beings a private property and this conclusion fell first on women. Prior to this women stayed home and tended the crops while the men went off to the iffy business of hunting. Most primitive societies were matriarchal as a result of this among other reasons, but the domestication of animals fell in the realm of the hunter. The property in animals became the property of men and with this change in property relations came patriarchy which dominates still.
Property in animals was also wealth that could increase naturally and so the difference between the haves and have nots increased with each new litter and this created the material basis for the development of slave societies. Prior to this, there simply wasn't a lot for slaves to do. In wars prior to this, a conquered people were either slaughtered or integrated into society. Now there were herds to be tended and an individual's wealth was limited only by the number of animals he could control. Now there was virtually unlimited work for slaves. Now wars gained an economic footing because the enemies flocks could be raided and the enemies themselves turned into slaves.
This was an absolutely necessary next stage in human economic and political development. These slave systems had to go down and be replaced by a new system then on the ascendancy, and if you'd rather be a serf than a slave you will agree that the lot of the laboring masses was improved. The Dark Ages is said to have lasted for seven hundred years so perhaps things could have been handled better. We can see from the current Libyan experience that revolutionary change doesn't always go smoothly. This was necessary because while slavery could again be made productive and profitable under conditions of large scale capitalist production for world markets and was well exploit in the "New World" by it, the requirements of relative self-sufficiency and small scale agricultural that existed in feudal times required a laboring class that was motivated more by the need to eat and pay rent in kind than by the lash. Feudal systems, systems based on land ownership came to dominate everywhere.
Technological development was propelled even further under feudalism and slowly but surely, in the workshops and burgers of the middle ages, a new form of production, manufacturing, was developing and it continued to develop until it could no longer be bound by the constraints of feudalism. There was a series of bourgeois revolutions in which feudalism was overthrown and capitalism was established. Under capitalism, ownership of the means of production, the tools and then the factories, and eventually "pure" finance capital became the most important forms of wealth. Land ownership had its limits but factory output could always be increased. The change from feudalism to capitalism also required changes in the workforce. The laborer was forced off the land and made to sell his services to the owners of capital for wages.
In its early period of ascendancy capitalism created many wonders. It created modern science and medicine. It explored and united the world although sometimes ruthlessly. It created modern communications and transport. In fact it created all that we need to live well and in harmony with this planet even as it stands more and more against the possibility. It multiplied the productivity of the laborer a thousand fold and created hitherto unbelievable abundance. For first time in human history the main problem was not scarcity, it was distribution. This puts us more or less were we are now with capitalism in an even greater state of decay and now threatening to hold back human progress in a way that could prove fatal to the entire species.
I use to think that the phrase "decadent capitalism" was just so much communist rhetoric until I understood capitalism as a system. The thing about all these systems, slavery, feudalism, capitalism, even socialism, is that as much as they each in turn may claim to be the be all and end all in its prime, each is just a social construct more or less appropriate to a certain stage of human development and as with the humans they serve, each has a useful life span. Each has a birth, a childhood, adolescence, and hopefully a long and productive adulthood before the very forces it has created and nursed to its bosom need to break out of its limits. This may lead to an agonizing period for the people who live in a system undergoing such extended death throngs but that is where we are now, making "decadent capitalism" an extremely accurate and inclusive description of precisely what is at the root of almost all our problems today.
Marx and Engels also understood that we couldn't just go there from here. The road from capitalism to communism must, of necessity, pass through a long historical period of revolutionary transformation called socialism. Under capitalism the contradiction between socialized production and private appropriation cannot help but grow. Socialism replaces the private appropriation of the already socialized production [thanks to capitalism] with socialized appropriation and control more in line with the current requirements of humanity. All revolutionary changes have required an intense class struggle between the ruling class of the decaying system and the representatives of the new class or classes in ascendancy. This is where the focus on the state and state power comes in, but the phrase "dictatorship of the proletariat" is generally misunderstood. Marx and Engels saw the state, first and foremost, as an instrument for the ruling class to dictate to the other classes. They, correctly I think, saw every state as dictatorships of the slave owners, land owners, or owners of capital, in governments that adopted forms more or less appropriate to the system they were ruling. They said that the working class was the new rising class under capitalism and the representatives of the new system, socialism, that would replace capitalism. They also said that the working class or proletariat overthrowing the capitalist wouldn't be the end of the revolution because the capitalist would try to re-establish their power by a million and one ways and would still have many advantages on their side so the workers would still have to exercise a dictatorship over their former bosses. But most importantly, Marx and Engels said that from the very beginning this "dictatorship of the proletariat" would be a state of a new kind because for the first time in history it would be a state in which the majority exercised a dictatorship over the minority and because of this it would even in the beginning cease to be a state in the usual sense and begin to whither away.
As we both know, the first attempts at implementing Marx's vision of socialism haven't been too pretty. What are we to make of that? I would first note that it has been so far tried only in countries least ready for it from the POV of really having thoroughly developed the "precursors" of advanced industry and a well educated working class. The reasons why those countries have been so stress by the decaying capitalist system as to attempt the leap to socialism early is "beyond the scope," as are the reasons why the workers in those countries with the best material basis for implementing a revolutionary leap seem most content to stay with capitalism. Let's just chalk it up to the law of uneven development.
But to point to these failures as reason enough to abandon the socialist project altogether is like pointing of all the early, pre-Wright Brothers attempts at powered flight or even their sorry first flight as excuse to abandon all attempts to build airplanes. We cannot speak of socialism without speaking of an entire historic era that is only now thinking about beginning. It could be hundreds, even thousands of years long. Nothing that has happen since the Russian revolution has given me reason to doubt the correctness of Marx's analysis, nor all the terrible things that have been done in his name.
I still remain a Marxist.
Call it what you will, a science, a philosophy, or a political movement, given that it not only predicted but also actively promoted an end to the current system, capitalism, and the overthrow of the rich by the poor, Marxism could not help but be attacked from all sides and intensely by capitalism. Among the most insidious attacks are those bourgeois force which have developed inside the movement itself, using the language of Marxist to sell a corrupt version of "Marxism" that is actually counter-revolutionary. This happened to the Russian revolution where a new bourgeois ruling class was able to establish itself within the "communist" party. Since then they have used their $$$ and influence to almost completely corrupt the Left in the western world. This is what we are up against with the Left in Syria. Their treachery is so effective precisely because they turn people away from the Left and that truly gives them nowhere to go.
So, I understand and share your frustrations with the "Left" as we know it today, and frankly I think most of these people are beyond saving because the first thing you are going to need if your really want to make it as a revolutionary is an intense concern for humanity, and most of these people on the "Left" have shown they would sooner ignore the suffering of the Syrian people than lose face and re-think long held prejudices.
I have taken the time to write this because I want you to understand where I am coming from when I say I'm a communist, why I think the "Left" has been so bad on Syria, but also why I think you should be careful not to throw out the baby with the bath water. I could say a lot more but I've gone on too long already so I'm going to go enjoy the beach now.