Pretty fun! Not too shabby of an idea and it feels very addictive and fun to go through all of the levels. It can get a little annoying when you have to retry: many of the levels have such a slow start that I wished I could have a fast-forward button to complement the stop button so I could get back to where I left off quicker. It's not too much of a problem as the levels are kept small and bite-size, but still, could help keep the pacing up. Also, some of the levels did feel a little out-of-order in terms of escalation, or seem to just be clones of already existing levels with minor things added on, so there could be some improvement there. Anyway, its a simple game, but the sense of speed and timing were really fun to play through, and I really liked the touch to turrets where it shows a bar to indicate when they are going to attack (I think that really helps reduce player frustration as they can know better how to time their stops and starts).