I've got a few minor notes:
- Changing the resolution doesn't seem to be handled too well
- The instructions in the beginning disappear too fast to fully read
- The result score probably didn't need three decimal places :]
It's a pretty simple but novel idea. I ended up building up a single level 8 shape and blew up everything else that dared to spawn, which got me a slow but steady rise in score... until I got bored of it and let things build, anyway. Didn't last too long after that.