I think I've been playing too much Alien Swarm. Since it's release 2-3 days ago, I've got 22 hours of gameplay, according to Steam. Doing my best to get all the achievements. Note the progress through the campaign on insane difficulty, which has proven to be the most enjoyable thing I've done in the game so far. It certainly isn't easy though, we've had to be really strict with our strategies. Which hopefully will help anyone else who's trying to do the same thing.