Skyrim has the most content and you'll play it the longest willingly,
If you didn't ever play MgHd collection it a great combination of games, peace walker in particular
Depending is your pc or console get BF3 if you have a decent pc, if not id say Dark souls.
Dead space 2 is likely now the cheapest of the bunch so i'd say get it to, geat 3rd person action, but the multiplayer is sad.