I've been playing some more L4D, and the game is still fun, but it does have some serious flaws in versus mode.
1. The worst problem is the /kill command. Originally intended to deal with situations where a survivor has glitched into an area he cannot escaped or be reach from it turns into a griefing tool. It instantly lets a player kill their current character. Your team mates will sometimes use it if they get pissed at losing or you try to vote kick them for being incredibly bad. The enemy will sometimes use it in a 4v3 situation by temporarily joining your team, killing off one of you characters at the start, then rejoining the enemy team. IT's a highly abusive tool and I have never seen it used properly before.
2. Not being able to select servers or view server information. The first issue being that occasionally your group will end up on a server with a terrible ping. This is a rare issue, but annoying when it does as everyone must now vote to return to the lobby. The greater issue is that you will occasionally join modified servers, and there is no indication that they have been modified until you encounter the problem. Some variations include :expert mode zombies (ouch), early tanks, no witches, random health reductions, multiple tanks, etc. The game applies it evenly to both team, but it can still be highly frustrating.
Otherwise teh game is good, and fun if you are playing with friends or competent allies.