1) The head is too small and it should be more rounded.
2) It's ears are a LOT bigger, I mean the pink ear is almost as long as its head and the smaller one should be like a quarter size of the pink one.
3) The feet don't have elevation, they're flat.
4) The red part of the eyes are a bit smaller and the white part should be triangular with the eyelashes being completely black.
5) The upper feather in its tail (at least I think they're feathers) should be as thin as the middle one.
6) The body is just a bit too chubby, shorten and round it up just a bit more.
7) This one is optional but I think the shade of gray of Sneasel's body should be much brighter. And I say it's optional because Gamefreak has changed Sneasel's color from brown, to almost violet, to a really dark gray and now to a bluish gray. I think it's your choice but I believe it should be like the actual modern model.
I think this is a great model and with some more tweaks to it, it will be relatively perfect. Keep at it you're doing a great job!