So, this thread is sort of old, but having done a project on Communism in my senior year of high school, I feel a desire to share my knowledge!
Communism is not a system of government - it's a means of structuring society in which there exist no social hierarchies whatsoever; in other words, everybody is equal. The ultimate goal of Karl Marx's theory is to establish a society in which the members of this society work together and share the fruits of their labour equally. There are to be no Kings, Presidents, Czars, Capitalists, Factory Owners, etc. There is no government in a Communist society. In a true Communist utopia, there'd be no need for such things.
So I guess my point here is that there is this BROAD misconception of what Communism is - when people think of Communism, they think of the USSR. That was NOT a Communist society - that was a totalitarian/socialist state; every single "communist" state that ever existed was actually in the "transitional" phase on the road to becoming Communist. To grossly oversimplify Marxism, 2 things needed to happen in order for Communism to be established:
1)Overthrow the bourgeois regime that is oppressing everybody (killing them is okay, they are bad men, after all!)
2)After the revolution is over, a group of dedicated revolutionaries would select a single individual to oversee the transition of society from a capitalist economic structure to Communism, known as the "Dictatorship of the Proletariat"
As for what a Communist society would actually LOOK like and how it would actually FUNCTION, well Marx couldn't be bothered with trivial bullshit like that. He just loved to write about how oppressed everyone was and how it would just be so fucking rad if all the capitalists died one day. What's wrong with it? What, apart from actually establishing the damn thing? If you look at the TWO major "communist" societies of the 20th century, Russia and China, there attempts to transition to Communism lead to deaths of over 60 million people; strangely enough, A LOT of those, and by a lot i mean, literally ALL, of them were workers - the very people the system of Communism is suppose to be for.
And finally, the main problem with Communism is that such a concept only exists in people's minds. It's a fantasy. How could such a society function? Hell, not even the guy who CAME UP WITH THE IDEA IN THE FIRST PLACE knew! That should tell you a lot about the merits of Communism.