Sonic Adventure 2 resembled Sonic Adventure in shallow ways, but the level design philosophy was entirely different and Sonic's controls had changed quite a bit. SA1 feels like an honest attempt to have the original gameplay in 3D, whereas SA2's levels were more straightforward, had more set-pieces, more Boost Pads, and Sonic couldn't even roll. SA2 feels sorta like a middle ground between SA1 and Unleashed to me.
Rolling used to be Sonic's signature move and even in SA1 it often came in handy if you knew what you were doing.