I played the modern Sonic (first 3D one I've ever experienced) and thought it was dreadful. Probably takes a bit of getting used to though.
I've seen some later playthroughs and the 3D stuff looks a lot better there. They've even got more of the multiple path stuff going on, which was always integral to the series.
My main dilemma is figuring out which platform to get it on. PC is much cheaper but I don't like the d-pad on the 360 pad and I'd probably need it, whereas my PS3 seems to be crapping out now.
Not that I need to buy it right away though. I've got Bastion, VTM Bloodlines and possibly DCUO all lined up. Plus, Uncharted 3 once I sort my PS3 or get a new one, and then Arkam City very soon. Argh!