Level 3 was too much of a step up.
Levels 1 and 2 were pretty easy, but then level 3... WOAH!
You should really have a more gradual change. Maybe have every single mole slightly faster than the previous one, and then after 20, the speed might drop suddenly by about 9 mole's worth... You know what I mean, surely?
Also, the 'centre' of the hammer should be moved up a bit. I think it'd feel more natural if we were using the yellow part to aim rather than a little crosshair.
Still, it's a well-programmed little game.
Good work. :)