I loved this game, enough to beat it twice and aim for all the PSN trophies to make it last as long as possible. In retrospect, collecting all the shards and doing all the stunts probably decreased my enjoyment of it and I should have skipped them, but anyway...
I almost skipped this game based on the demo, which was really hard and just wasn't fun, but the full game eases you into things very cleverly, introducing each power one at a time and giving you a whole linear section to put it into practice. The powers themselves aren't too original (they could be weapons: normal gun, grenades, sniper rifle, etc.), but the controls are very smart in that your whole arsenal is at your fingertips the whole time. No need to change your equiped weapon, just press the right button.
The story was fun though a little disjointed, and perhaps the side missions were a little repetitive, but moving around in the game's world was just fun. Climbing everywhere, grinding on rails or power lines, gliding in the air, it was all pure fun.
I liked the game so much, I picked up Sly 2 and 3 on the cheap recently. Just started Sly 2... it's fun, but it's not Infamous.