Very creative, lots of fun. The game is tailored to the player, who can finish each level pretty much in any way they wish to. I have no problem with the grading system, but I don't really like the overall time limit. It kills the game for those who wish to get through some of the levels using stealth and patience. there were a number of tactics that I simply couldn't use because the levels are timed, and that did limit my enjoyment.
Good challenge, though. Later levels are very confusing and challenging.
Overall, a very good idea.