Sonic Riders... yeah, it looked kind of neat, but the only time I played it was real quick on a demo at Game Crazy--more like fiddling around, really. Granted, I didn't have much time to get used to the controls, but what I played was... okay (how it got a sequel with the reviews--and no doubt sales--it garnered, I'll never know). As for Sonic Heroes, that was the first Sonic game on the GCN that I full-out balked at getting, perhaps ironic because, as a young, impressionable gamer, I bought Sonic Adventure DX and Sonic Adventure 2: Battle, games which, although not outright bad, I would probably not seriously consider were they not re-released until today.
(I also bought Sonic Mega Collection and Sonic Gems. Though the latter is somewhat mistitled, it's not that terrible, if only because of Sonic R's so-bad-it's-good vibe that has lent my friends and I many a mirthful get-together)