Great?
Honestly, I don't know how Sonic the Hedgehog can still have a fanbase. How many terrible games does Sega have to release (with very few exceptions) before people just stop buying it already?
After Sonic Colours, people seem to be more hopeful. I played Generations a bit, seems good enough.
Alright, so Colors is one of those exceptions. Still, there was Sonic Unleashed, Sonic 2006, the Wii Games (Arabian Nights + Black Knight, i think they are called), Sonic Riders, etc. beforehand.
Any other franchise not riding on the curtails of nostalgia (that would be my guess as to why people keep buying it) would have bought it after just one of those games, let alone all of them.