First off, I want to say that, never having actually seen much official Neopets artwork, the technique here is really well handled.
The characters don't look like they could have been drawn any better, and the shading is spot on.
Being as it's a fanart though, I wasn't sure how to handle the originality category.
But the characters' exressions added a sense of originality that is completely your own.
The only suggestions I could make is that, while all the other characters are entirely in frame, the cat wizard dude is slipping out a bit.
It might have been better to exand the picture a bit so that the whole character could fit in.
(As opposed to moving all the characters up higher, which would have made it look a tiny bit cramped.)
Anyway, that's about it.
Fantastic work, overall!
Hope you don't mind my nit-picking