I really don't care for RE4's controls, but that game was optimized for them, so it bothers me that RE5's team really didn't get it with their game.
I like both type of games. L4D purely for a great co-op FPS, RE4 and Dead Space for their single player focus. I like variety. I don't plan on playing RE5 co-op, as none of my friends are interested in that game, it's also not why I want to play it, and I wish the producer/director had been shot before they could execute it. Well, I wish the real RE team could have worked on it, instead of the Capcom left overs. 😱
Playing L4D with my 3 friends was quite a bit of fun, but after we beat every level to death and play time kind of died off. I like that game still, but one of my friends is a curmudgeon when it comes to it -- I had to buy him a copy to get him to play, so we rarely play these days. Anyways, because of that, we haven't played it in a while. It also doesn't help that DOTA is still our favorite online/co-op game and gets the majority of our time, at least until BattleNet released an update that killed all JAS enabled mods last week. 🙁