Thank goodness for demos. I guess I was suckered into the Sonic Cycle this time (I never caved in for any 3D Sonic games since Sonic Adventure 2) and I was pretty eager and optimistic about this game regardless on what I heard or seen prior to the game's release, but wow, I think its an insult that they called this Sonic the Hedgehog 4. It's not a terrible game, but it shouldn't be considered the spiritual successor to the Genesis Sonics.
I think the graphics are fine, I do like the clean look of the game, though I do think the videos out there of the 2.5D Sonic remakes look even better, but I don't have any problems with the look of the game. My only problem is Sonic's full speed run animation looks a bit awkward and I hate how he spreads his arms and legs whenever he comes off a ramp. Otherwise, the look and level design felt like a Sonic game.
I haven't heard much of the soundtrack except for the 2 songs in the demo, but I think its okay. It pays some homage to the old Genesis music, but I didn't think they were as catchy as the previous Sonic games, but of course, I haven't heard the rest. At least it's not the Sonic rock music.
And of course, what majority of people are complaining about are the controls. Just wrong. I'm in disbelief that they couldn't get that right after all these years. All they had to do was download any of the Sonic games on XBLA, Virtual Console, or PSN to find out what it should be like. Perhaps it was their intention to make it "fresh" for the new generation, but for a project that they seem so dear on going back to its "roots", it's hypocritical of them to change so much of the controls and physics of the originals. The controls aren't unplayable for sure, but it just doesn't feel right. Especially if you're someone that owns Sonic 1, 2, 3, & Knuckles, then jump into 4; it's hard to adjust to what you're comfortable with and what everyone feels how Sonic should move in 2D. I don't even think Sonic Rush has this physics, but I could be wrong, I haven't played that in a long time. At first, I didn't believe in what people were saying on these forums on how they could mess up the controls, but they certainly did; no exaggeration about it.
Also, I'm not so sure about how they're going "old school" for this one where they wanted it to be more similar to Sonic 1 over any other Sonic game. I thought the progression in sequels usually builds upon the previous one. Like how levels got bigger over 2 and 3&K, how there were storytelling elements added, the addition of new power-ups, Tails (2-player coop), etc. But this one, they went backwards where it just seemed that they were too afraid to add too much because they knew they'd mess that up even more, but the improvements is what I looked forward to from each iteration of the Genesis Sonics. Sure, they added homing attacks, but it felt the game was too easy with that, which again, could have been their intention. I would've preferred them going back to the different shield mechanics from 3&K as it kept it interesting on depending which shield you had allowed you to explore different areas and added to the gameplay. Perhaps in Episode 2 (if they even make it), they'd bring these things back, but it was disappointing to see that there wasn't anything new or any previous power-ups that were retained in this game besides the original shield.
Yes, its unfair to make judgment on a demo, but I think I got a good idea what the rest of the game will be like and from reading plenty of GAF's rants, my assumption is probably not far off. I think on its own merits, the game seems okay. I'm just more disappointed with it that they called it "4". This really should've been a new spinoff if they really wanted the Genesis Sonic fans to get off their backs on this, but they took the risk and opened the can of worms and this is the result of it. I would consider buying it for $5, maybe $10, but not $15 as this is not the Sonic game I waited 16 years for.