I started playing the game last night. it's fun, but i can see why the game is not fairing so well in modern reviews. It's lacking the gameplay polish that modern day games are expected to have.
The art style is beautiful, the level design is creative. The hub world is awesome, and reminds me of hub worlds from older 3D games I've played in the past. Where the problems start popping up is the gameplay. The controls feel a bit odd and the game feels unfairly cheap at times. Problems that most likely would of been taken care of if SEGA didn't layoff the studio earlier this year. Gameplay polish is usually one of the last things taken care of in a game. There is also some framerate issues too, but nothing game breaking.
I've never played the original, but I gave the one on PSN a bit of a go, it did seem to have better controls then the remake, but I didn't play it for very long, just coudln't get into it. I think that's the thing with a lot of old games, if you didn't grow up with them you probably aren't going to be able to get into them unless you're a huge fan of retro games and can deal with looking at pixally graphics on a HDTV.
If you are a fan of platformers the game is definitely worth a buy, you will probably enjoy it. Just don't be expecting a super polished experience.