I just got it today and I need to tell you that it is amazing.
It is quite similar to the first Infamous (which was also amazing). This gives it a nice touch of familiarity without making it feel repetitive.
The combat is fun. The graphics are great.
The Amp is a nice add on to melee weapons and close combat. The combat itself is good but the Thunder Drop (the one where you jump off a building and whack the ground) is fairly inefficient. The Static Thrusters always come in handy.
The two sides of karma is also fun.
Overall, I think that it is a very good game and every PS3 gamer should get it. It's free!