Prototype is an open world action game developed by Radical Entertainment (an Activision studio). Release Date is 6/9/2009 coming out on the PS3, Xbox360, and PC. Check out this missions video to see what it offers:
InFamous is another open world action game developed by Sucker Punch and published by Sony Computer Entertainment America (SCEA). I see a lot of similar and dissimilar elements to Prototype. Release Date is 5/26/2009 coming out exclusively on the PS3.
Check out this developer video to see more about InFamous:
Both games offer a range of techniques and more freedom to the player to explore how to accomplish tasks.