VERY nicely done... though realistic Bun Bun's always throw me, Pete's simple style is so iconic, it looks like they spared no attempt to get incredible details in.
Personally, I'd have tried to go with all black eyes--and been more subtle on the mouth, since Bun Bun rarely ever shows white in his eyes and the fact his mouth seems to be non-existent and his emotions are always in his eyes are pretty crucial to his unnerving unreadability unless he's REALLY peeved.
But Pete HAS shown both at least once to be fair.. I was surprised to see whites in his eyes here, 2nd panel on the bottom (
http://sluggy.com/comics/archives/daily/110915). And we saw his mouth, and teeth gasping for air in Roken.
So yeah, maybe I'm just nit-picky, Bun Bun fanboy that I am. Respectful critique aside, its VERY nice work-- one of the best fan-portraits I've seen, and enough to grace my desktop for a full season. :)
PS- just saw the stars worked in... NICE.