You know, coming off of my monologue's about my problems with Classic Sonic's model in Generations, I think I've also put my finger on what it is I didn't like about the model they used here - outside of just basic aesthetic principles, because it does look pretty ugly on that note, as well.
My problem with it isn't that they tried to blend Sonic in with a real world environment, because that can work and be potentially pretty interesting - but, just like Sonic '06, when doing that with a character like Sonic who is so inherently "other" you're constantly going to walk over the Uncanny Valley on a dangerously thin path, particularly because we have something that looks and moves in a recognizably human way within the same frame. You have to, you know, be able to actually pull it off, because this is kind of one of those things that we know from trial and error can't be excused because of low-budget or whatever. And, I think the problem with both of these, in this context, is that they decided that they were just going to port Sonic's surreal, "silent animation through a cartoony Japanese lens" design straight over and base their character model off of the ones being used in the most recent games, and set them right next to live people. This doesn't work, because of what I mentioned previously, but there's an easy fix that I'm not sure why Labron and co., didn't take:
I mean, first of all, figure out what to do with his mouth, because Jesus. But, outside of that, really - all they had to do was to give Sonic some kind of physical definition, an underlying musculature. Nothing that changes the silhouette of the design or what is inherently "Sonic" about it, but something that at least lets us know that this is a character of flesh and bone like the rest of us, because as it is he kind of looks like an alien, and is entirely separate from everything else in the film, which is the problem and the thing that colors the entire film. It looks cheap. Just flesh out his arms and legs a little bit, and give his torso some kind of definable shape. Also, in keeping with that, maybe make the shoes and the gloves a little less cartoony - There's nothing wrong with a little change, and I feel this probably would've helped a lot. It would've given the character a physical weight and heft within the world Labron was trying to set up that was missing. And, while I'm not somebody who really has a preference either way, I do think that using Sonic's classic design would've helped, because it's a lot more malleable in this respect. I say this because there's one artist in particular who used to work on the Archie series who did the very same thing I'm talking about in the mid-nineties, and it's probably one of my favorite designs for the character besides Oshima's original sketches, overall. I can't remember his name, so it might be (haha) Ken Penders, for all I know.
And personally, I even like the "styled" approach to the spines, in theory if not in execution, because that's something that's always been implied to be true about the character.