I agree strongly with althaj. The rewind feature should have been the core of the game, but it felt pointless and useless, I never felt I had a good handle on it at all and never used it to beat any levels. It just boiled down to an Angry Birds-like little physics game.
I think each grenade should have had a timer on it, a bar or numbers ticking down, color changing from black to red until it explodes, something.