What the hell are you doing? Go out and buy this game!
Gameplay is repetitive but never loses the thrill. Graphics, maps, sound all solid, characters loveable and wonderful.
Absolutely no storyline, just a co-op game to play with your friends, and good ol' solid fun. Remember that thing we used to buy games for? Fun?
Well yeah, it's back. The maps get a little repetitive, but Valve will come up with new DLC soon enough. In the meanwhile, play Versus! Never gets old.
Swap between survivor and infected, and beat the other team's score. Just good old fun contests. Playing as the infected is bloody awesome. You just have to try it.
Just a note: the difficulty setting is not REALLY just right, I just chose that option. The difficulty varies greatly to suit you.
Now go buy this game, find three other mates or just join some randoms, and play like there's no tomorrow.