Which video games should I add to my collection?

From personal experience, I would get Resident Evil 5, Left 4 Dead 2, and Fable 2 to start off. Those three are some of the most fun games I've ever had the pleasure of playing. Resident Evil you play as Chris or Sheva and try and find out who's behind the infections in Africa. Fable 2 you follow/make your own storyline, and choose your own path practically, and Left 4 Dead 2, you just get to shoot a lot of zombies. All of them are great fun, especially for multiplayer(with the exception of Fable 2, that's more single player)! Resident Evil and Left 4 Dead are games you can enjoy playing by yourself or with a buddy of yours.There are lots more games that you mentioned here, but these three would be my suggestions to get first. Keep in my mind, that this is only my opinion, and that this is from my experience, and even from some others' opinions. Happy gaming my friend.