We're coooool cats!, Ah. Love the music and how as you gain more people you get more layers added into the sound track. It had me singing along and snapping my fingers towards the end.
Unfortunately I think I lots too many people along the way and was never able to make it to 25 members. Also it would be cool to add more visual feedback to the rhythm bar for hits and misses.
Great idea through, I wonder how you could expand upon it.