Hope I'm not too late here....
But I LOVED the demo, sure it was glitchy in spots, but I'm sure you'll work that out.
It really felt like the true "Sonic 4", I felt like I was actually playing an official Sonic game from the 1990's. I can't believe some people on here were actually complaining about this game.
One of the things I loved most was how Eggman interrupted Act 2 to blow up the island - that is something like Sega would have done back in the day of S3&K.
Again, really awesome, I was extremely impressed - hope this gets finished, I can't wait to play the full game!