I do agree with Lark there. A few sections feel clunky. For one, sonic needs to be a bit quicker when pushing a block. Plus a few sections, you try to jump, and you end up hitting the ceiling, missing your jump and plumting to your death. Mainly marble zone.
Plus when I paused the game it just froze. Dunno what happened there. And none of music files will work :?
Aside from that, it's good game. The art is beautifully done, sonic has some nice animations, music is very good, and the game has a great art style. Not to mention the bonus features, like extra levels, and being able to use the classic sprite are great additions. Iron out and the problems and this will be a great game.