Swan is right on a few marks here.
First off, the community is filled with douches who bitch and complain that you don't lick their balls and play exactly like they do. (I call these "lifers", to reflect the fact that they seem to think gaming should be taken ultra seriously like it was a real-life issue of importance rather than a diversion coupled with the fact that they usually spend ridiculous proportions of their life playing their game of choice.)
Second off, playing solo sucks because the AI is generally retarded, although they are good for wasting their heal packs on you and not other people.
Third off, it CAN be a seriously fun and scary experience, especially when you wear headphones. Few games will make me literally start or jump in my seat, but Left For Dead will from time to time. It has a great ambience and a solid replay value. The real challenge is in finding a few people to play with that you don't want to fuckin murder on principle of their complete selfishness, arrogance, and general lack of any redeeming human qualities.
Nothing, in my opinion, is more annoying than a gamer who not only dedicates huge portions of his life to a video game and takes it entirely too seriously, but who continually insists that you do the same and berates you if you don't. When I walk away from that nonsense, they call it a rage quit. I call it having good sense of putting myself into environments worth being in and not wasting my time on shit-stains. After all, if you spend a lot of time near shit, it's hard not to stink. :S
PS, I also played it on Xbox, and it totally sucked monkey cock. Best way to start off is to play on normal or beginner and just get acclimatized to the game. Much like CS, you need to learn the maps and the tricks to them before you can pwn it up, not to mention that some of the missions in L4D2 are retarded hard no matter how good you are.