inFamous is definitely a breath of fresh air for sandbox world games.
Having the ability of superpowers, which only grow stronger and give you more abilities as progress further through the game is definitely rewarding. The good thing is with all of these super-human powers, your not too strong for the game. The game hits you with the right amount of bad guys/missions that will test your skill. Heres the good and the bad.
The Good:
-Running around with the ability to control lightning zapping everything is really cool.
-Story keeps you glued, very critical in "sand box" type games, very interesting endings.
-Game is very rewarding with its wide array of side/regular missions, mixed with your karmatic decisions on whether you should help someone or steal from them...
The Bad:
-Once beating the game in both good and bad scenarios, not much left to do... loses value.
-Graphics could be better
Overall, I would consider this game a must-have, even if your not a big fan of sand-box style games. This is a good one.