It's nice, fun!
It's a pretty fun little loop =D
Loops smoothly, really well done
Though it doesn't sound much like a boss theme... But that depends on the game and on the boss, so, I can't complain =P
That explosion also sounded a bit too loud...
Also, the song is pretty short, and after one loop, it starts to get boring =/
Try to make it longer and vary more :D