…I know there was SOMEone that I found disappointing… but off the top of my head I can't recall who.
EDIT: Oh, it was Spiritomb. I've always hated how disc-like flat and cartoony he looks in the 3D games when, on seeing his Sugimori art, I always imagined him as a swirling cloud of malcontent… Not a… swirling disc with a liddle rod up his arse. Bleck.
EDIT 2: Oh yeah, Torkoal was another one. I hate that his smoke cloud is apparently a part of his model, it just looks cartoony and awkward. Koal looked MUCH better in Colosseum, where he was just a tortoise that occasionally puffed smoke from his back or nostrils.
Eelektross. In BW it seemed large and menacing, a giant electric eel/leech getting ready to attack you.
Now... it's tiny, and it looks like a tapeworm. I thought it was its pre-evo (Eelektrik?), that's how small and un-threatening it looked.
Apart from that one, though, I have yet to see a disappointing model.
I disagree. Eelektross was cool in BW, for sure, but its goofy habit of hopping around around on its liddle footfins was about as far from intimidating as you can get. (also, hopping is not 'levitating'… just sayin')
You know what it looks like now? A lamprey. Hmm myep. That works.
Personally I think it's eerier and more alien than ever now, which is plenty intimidating enough for me.