I was thoroughly disappointed with this, myself. I mean, the changes were minor, even for a Street Fighter II upgrade.
My particular beef were the animations, because I don't think Udon's work compares to the original sprites.
For instance, Ryu's original standing sprites, and the new ones drawn by Udon. They stayed far too close to the original specs, so the Shotos' standing looks incredibly odd-looking because the belt randomly jumps around. The animations have been made even more dated in appearance thanks to this folly.
Another beef is the mismatch of styles. In the foreground, we have two canyon-muscled Guiles standing against a backdrop with... Anime-faced characters present? How the heck does that match a general style?
To top it off, a lot of the backgrounds lost their luster. For instance, originally, Dhalsim's stage had only two elephants trumpeting in the background. Only two, and the rest would pipe up in order when a player won the match. But instead, Udon decided to make Street Fighter II look even more dated by having every character and object in the background animated at the same time.
Street Fighter II HD Remix's only shining point is the netplay. Other than that, everything else is "Been there, done that so many times".
Yes, the hitboxes ARE kind of nuts. I think in some cases they're even out of scale!