M2's 3D Sonic the Hedgehog just came out on the eShop for the 3DS today here in America. I think the 3D looks really neat with this one, it runs really well and you can access the stage select right from the bat with the "Special" option, which is handy. The spindash works great and I haven't experienced any slowdown yet, even with the 3D on. I know there's a million Sonic 1 ports + Taxman's version but I think this one is worth grabbing as well.
M2 announced a second line of SEGA 3D Classics that they are now working on, I'm certain Sonic 2 will be one of them, so we can probably look forward to that.