I know that most of the people here hated on it, but I really enjoyed the demo -- regardless of some smaller issues here and there, they have nailed the overall feel of what makes Sonic fun, at least for me. I also really enjoyed creative use of the homing attack to extend spring jumping sequences (bounce off of multiple enemies in a row, etc).
I also really like the music to the first stage, though I'll admit having a preference for Gecko's Genesis synth version. That's nostalgia getting in my way though and I acknowledge it.
If Colors is of this high of quality or a step beyond, then I think Sega will have finally brought Sonic up to speed (pun intended) with modern technology.