I've played this demo 10 times already, so I guess it's time to talk about it in more detail. First things first - I'm not playing with a playstation pad. I'm playing with a Sega Saturn USB controller, and good god is it amazing. I can't recommend the pad enough, it is by far the most used controller I've bought this gen. But enough about that, let's talk about sonic.
First, rolling - it is indeed true that rolling doesn't unlock hyperfast mode like it basically used to do in the old games, I think many (myself included) got the impression that rolling was broken to the point where it fucked up the game. It doesn't. See, when you roll, you don't gain speed... but you don't really lose it immediately either. It's not like when you roll you come to screeching halt or anything. Rather, rolling feels a lot like running now. And in fact, just when you'd expect that you'd start slowing down, if you continue to hold forward, you'll actually come out of the roll and continue running.
Now before everyone shits themselves with anger, it's not really bad. It's hard to explain but it doesn't really feel unnatural. Overall rolling isn't as great as it should be, but it's not an all mighty sin. If this winds up being the game's biggest flaw, then we're in for a great game.
Now then, momentum - the physics feel different from the classics, but familiar. That is to say it's not 1:1 (it's DEFINITELY not 1:1 in fact, no where near) but what you're playing evokes memories of the old games. It takes a few jumps to get used to, but I got the hang of it extremely quickly. The quirk with this game seems to be the exact opposite from the physics quirks of Sonic 4 - you have to completely commit to every movement you make because momentum will keep you going. Jumping is basically the exact opposite of what it was in Sonic 4 - if you try to move around in the air and really correct your jump, you're just gonna screw yourself up. The best way to play, I've found, is to just let yourself go and completely give in to your momentum. So like, you're running full speed and you jump at a buzz bomber - don't try to adjust yourself to make the attack connect perfectly, just go with the flow and accept that the momentum is gonna throw you into the badnik.
My first run, I found myself constantly trying to correct my jumps, and coupled with the fixed bounce height, it doomed me to the lower path. But on subsequent runs, as I adjusted my playstyle, I found that I didn't need to correct myself, nor did I need to worry about what angle I hit the badnik from specifically because of the fixed bounce height. It just all sorta works.
Now, realistically, the most annoying aspect I've found is how springs behave. Others have touched on it, but springs really sort of lock you in place as you're propelled upwards until you're near the apex. It feels weird because it's not at all like the old games where you had a lot of flexibility when you were springed upward, yet it's NOT automated so you get this feeling like the spring segment you see before you might not work. But... it kinda does. I dunno, it's very hard to explain. As more people play maybe they'll expand on what I'm talking about.
Now, despite my length at describing these... sorta-kinda faults, don't mistake what I'm saying as bashing the game. This feels extremely solid. Easily the best feeling sonic game I've played in decades, literally. As a successor to the genesis games, it gets a whole hearted thumbs up from me. I can't stop playing green hill zone, it's a ton of fun. And the physics make it even more fun.
Oh and one other quick note - the instant spindash? Those of you who worried that you could spam it like in sonic adventure? You can shut those fears down right now, trying to use it like you used in SA will fuck your speed run up. When you hit the spindash button, what the game does is basically stop you dead in your tracks, makes you duck, and start revving. You instantly lose all inertia. The button is basically a macro. It's impossible to use in conjunction with running.
All in all, this game is a hell of a lot of fun. I cannot wait for the full version. I give the demo a solid A. Fix the issues with the springs, and maybe work on rolling a bit, and this will easily be an A+.