I was going to come in here and give my mostly positive reaction to the demo, but Sharky had to ruin everything.
Classic Sonic DOES feel amateur compared to Sonic 1, 2 3 and Knuckles, even some of the 8bit games have way better design. Go play some XBLA and PSN platformers m9t, even some average quality Game Boy games have very similar design. That is to not say it is a horrible thing (amateur design is a massive improvement from whatever the Hell stuff like Sonic 06, Heroes and Advance 3 was), but the fact you have to snap every time some points out their mild dislikes is extremely irritating.
There is a reason Modern Sonic stuff seems better to all of us, it is because Sonic Team is specifically gimping the Classic Sonic design and general amount of content. Only 2 bosses, only Sonic, Metal Sonic and Tails get classic skins (Classic Robotnik might only be on the signposts...) and 3 zones? Sonic Generations is a Trojan horse designed to appeal to a broader audience and make them think "The classic games were not that good after all". It is diabolical and brilliant. It is already taking effect and rotting our minds.
But, the good news is that Sonic Team will think they really struck gold this time and surely mess up the next few games (with the possible exception of Sonic the Hedgehog 4: Episode II, which I am seriously looking forward to), but most of you will be super hyped to play their next 30fps mostly 2D action game about aliens.