Very good
I loved the music in this game, although I was only able to listen to two of the songs (I'm one of those rythmically challenged people someone mentioned earlier XD). If there was one problem (and this is honest criticism), it was what happened when a creature got through. Specificlly, how it launches itself into the air. Maybe its just me, but whenever that happened, I thought a creature was coming in from above, so I attacked up and invariably let another creature through. If you could fix this, that'd be great. If not, well, I'll probably adjust. Thanks for the fun game!