It's not a straight port at all. It is based on the "Retro Engine"(which I guess was done by those at Sonic Retro or something). It's possible the game was rebuilt up from scratch, with things placed just like the original(not sure on this though).
Anyway, features:
- Sonic 2/3/&K-style Spindash
- Japanese Soundtrack(trailer indicates
- True Widescreen
- On multiple platforms
- And probably more.
Also SEGA claims it's a prequel to Sonic 4 Ep1.