What are some good games with huge, open, sprawling environments?

I like the kind of Games with big, open, sprawling environments. Games that have main missions and side missions. Games like Prototype, inFamous, Spiderman (1-3 and Web of Shadows), Grand Theft Auto (all of em), and Bully. I don't really know what genre these are classified under (platformer? adventure?). I'm not really all that into MMOs, but they're not entirely ruled out.

Could you give me some recommendations to PC games like these? Thanks!

You should play some RPG's, Try the Elderscrolls Series, Fallout 3, The Witcher, Star Wars KOTOR, Mass Effect. ferrari2001

Far Cry 2, S.T.A.L.K.E.R., Mercenaries 2, Saints Row 2.

First games that come to mind are ES4: Oblivion, FO3, Far Cry 2 (although it gets pretty repetitive).