Not bad, but does need some work
This game isn't god-awful, just bug ridden. The graphics aren't bad, although they do have some problems. The controls were responsive, if a little slow, and the game was fairly addicting and very easy to figure out.
However, there were some major bugs. First, there's the sound loop, which should take ten seconds for everyone to figure out. The fix is as simple as turning your speakers off, people. I mean, the sound isn't that great to begin with. Other than that, you can hide offscreen, which makes you invincible, and if you just hold down CTRL for continuous fire it won't kill the mice, they'll just keep respawning.
I don't know much about flash code, so I can't really help you, but those are the bugs that I could find on my couple of playthroughs.