It's ok for the first 1000 or so levels, then they seem to get greedy, introducing levels and promptly making them too difficult to pass without using power ups. Things like cutting the time plus silhouette mode plus fog, before you even have a sense of what the objects in the scene are. It's stopped being fun. It might be ok if they didn't artificially limit play time so you can try until you get it, but I don't like passing a level a week, and I'm not going to pour money in just to keep trying