infamous is a PS3 exclusive and prototype is a multiplatform title. Both are largely freeroam with a few set plot necessities. They are a bit set in a fantasy type universe (both main characters have mysterious powers) but there are no futuristic or old world based technology.

Another option are the Saints Row games or the Godfather games. Both center around a modern universe with organized crime at the center of the plot. Saints row is the most similar but may feel like a spin off. God father has a more unique feel.

My final reccomendation is an RPG but an in my opinion more action. Fallout 3 can be as short as a 10 hour campaign (if you speed through) or as long as (insert extremely large number here). It has three current DLC options (one raises the level cap and removes the ending to the game so that you can continue free roam). Again, yes it is an RPG but you can play it as a shooter, as well as a free roam game.