I'm completely flabbergasted. Not by the subject, hell, the subject is probably the least shocking in this thing. I'm just wondering how in the flying fuck you made this thing. Just Flash, you said? A-fucking-stounding. Style is completely right with some great colouring and monstrous design decisions. I actually somehow liked the faces from the audience more than the actual monsters.
If I had any criticism, it's mainly in the sound territory. This would have been so much more intruiging if you used sound effects instead of metal. It seems a bit of an obvious cop-out choice to have a song playing instead of doing the effort with good sound design.
Overall, kick-ass and sick animation. For the love of everything sacred, give us more.