Grab your Gun and Your Friends
The game is almost to unforgiving depending on the difficulty you play. While there are times were you will get frustrated to the point of taking the keyboard and whipping across the room, it's fun to see how things play out on your next run through.
Replayability is Left 4 Dead's greatest strength. I find myself always eager to play whatever level I find myself in, since there is a variety of environments between the 4 Campaigns' backdrop. And the AI director really does help to make every encounter you face feel new.
Left 4 Dead's downside is a lack of content. The ten weapons in the game are all fun to use, and you'll find yourself switching between them on the fly, but it would not of hurt to have a larger selection. And while the game has massive playability, some players won't help but find the 20 maps a little on the short side.
The Game is not meant to be played without buddies alongside you to scream at your every mistake, but the single player AI bots are competent enough to get you through a campaign. They to have their little problems, being unable to wield grenades and are overly eager to heal you and save you from danger; often compromising their own safety in the process.
The versus mode is probably one of the most unique takes on competitive multiplayer I've seen in a long time. The mode completely changes the rules of the game, and survivors rush frantically to make it as far as they can to score more points; and it feels good to be bad as the zombies and ruin the survivors' good time.
I would instantly recommend this game to anyone I know. You might think the lack of content is not worth the entry price, but once you find yourself absorbed in the game, you won't want to play anything else for a long time.