Wasn't impressed at all.
I thought it looked like the Mega Drive games and was going to play like the Mega Drive games and was going to be a fun sidescrolling experience. Instead, it sucked.
Gameplay - The first level of the game is called Splash Hill Zone and it is almost exactly the same as Green Hill Zone. I play new Sonic games for different levels, not the same re-hashed level with a new name. The physics in this game is what really lets it down. The whole point of the 16-bit games is to gain momentum and roll up hills and into enemies, instead Sonic can literally walk up hills at a snails pace and you gain no momentum what so ever. This just doesn't feel like the classic games at all and frankly is not fun. There is a massive choice of 4, count it, 4 levels. All of which are re-hashed levels of Mega Drive games. Splash Hill - Green Hill, Mad Gear - Metropolis, Lost Labyrinth - Labyrinth Zone without water and Casino Street - Casino night. This to me just seems incredibly lazy. Not to mention there are 3 acts each stage so it gets really old, really quickly. Also the homing attack is in this game. In a 2D sonic game it just defeats the purpose of the jump attack and makes the game too easy.
Music - Not the best music ever but not terrible. Every Sonic game that has ever existed has at least 2 very memorable songs in my opinion (Even Sonic 06) but nothing comes to mind in this game.
Graphics - The graphics look okay I guess. For a 7th generation game, It's what you expect really. Sonic looks too blue to me for some reason. It kinda bugs me but the backgrounds are quite nice so I tend to look at the level more than Sonic.
In conclusion I think the game is simply a load of s**t. I don't see the need to make this game since it is essentially a 16-bit game with terrible physics. The dull music doesn't make it any better and even the ability to turn into Super Sonic during levels doesn't make me want to play it. Part 2 has been announced and it will have the same physics...Which makes me wonder what the hell took them so long to make it ?
Anyway the level design is decent I suppose so It's not the worst Sonic game ever but I would give it overall a 5.5/10