So I've been playing a crapload of Left 4 Dead (PC) these last couple of days. I've won the demo on Expert 4 or 5 times now, and I've found a number of things that work. Here's my first tip.

When you know a horde rush is coming (usually the musical cue), get somewhere narrow, like a hallway, stairway, or subway car. Have each end player crouch facing their respective end, and simply use the melee attack repeatedly. The two middle players face towards their respective ends as well, and shoot the stunned horde. Do it well, and the zombies may not even be able to touch you.

Do this and you might actually survive a horde rush on expert without a pipe bomb.

I got a chance to play it again yesterday was discussing this very thing also. I think it will be good to have a repertoire of different tactical formations and call them in with codes during this game. As well as use the environment to your advantage whenever possible. Cars seem to be useful as a vantage point to take long distance pop shots while others do the doirty work. If you use them cautiously and pan around well.

I can't wait 'till the games comes out fully; then my mates can form some stratergies like this and be able to pull them off. When you join a random team that doesn't have a clue it's really annoying - people running into your line of fire, shooting willie-nillie at anything they see (even if it's you), hogging all the medipacks and pills or people not bothering to rescue you when a Smoker's grabbed you or a Hunter's pinned you down.

I've found a few people during my random games that know what they're doing and it's a hell of a lot of fun then on expert, except when a Tank comes; in which case you're more then likely to die with your team.

nice tactic man. I'm struggling to pass it on the highest difficult, but that is part of the fun. Normal difficult is a joke, Advanced is pretty easy as well, but extreme ( i think its the name ) gets really hard if you don't have a good team