2D, although I think the 2D Sonics are also pretty mediocre compared to other 2D platformers. They're mostly an on rail platformer. The 3D games all suck in my opinion. Bought Sonic Adventure 2 and the DX add on content on the PSN when it was on sale at one point because it's such an amazing game, etc, etc, quit after playing through two levels. If people love Sonic Adventure 2 so much, not sure why they don't like Sonic the Hedgehog PS360 as they're both just as bad in my opinion.
Well, Sonic 06 is much worse because it has many annoying glitches, the story is complete crap, the mach speed sections are unplayable, you can't even jump on enemies to kill them and other things.
---Member of the official Squeezol Fanclub---