Large File Size
The characters are great, but the flashes are boring. Also, they have that tendency to be real short with very long mp3s attached to them, making what should be a 75 KB file 2.5 MB.
Put these guys on some sort of adventure, and make sure they never get impressed by anything while on the adventure.
Read up on the audio optimization FAQ on Newgrounds. Either don't have any music or make a short loop.