I believe I've figured out what's causing levels to hang. When spawners do their... spawning, and their spawns hatch from those bubbles, they come out, and SOMETIMES, one or more walk off screen out of the boundary. If it doesn't come back onto the screen, and isn't killed, the game will not register it's end game requirements of Either losing all lives, or killing every monster, or a mix of the two.
:[ Please address and fix this.
Davis007, this happened to me too, and it's really upsetting... It's the level where the right side and the bottom spawn and approach the top left corner.
I liked this game RIGHT off the bat, due to the achievements and killer physics. Two things though: As BreadFish mentioned, notifying people when they got achievements would definitely be a good feature. Also, badges are a necessity :3
The key is, once you feel that it's too fast for you, run into things to make you slow down a little. Don't slow down too much though. Easy way to get Way beyond 5000.