Unfortunately, on the DC side, I have been mostly a collector and not so much a player. Some I hear mentioned on a regular basis are Shenmue, Crazy Taxi, and Jet Grind Radio from a fun game-play standpoint.
I have also seen youtube footage of something called Segagaga that never made it to the states, but is essentially a parody of Sega's going out of the console business, programmed by their people in the waning days of DC. The youtube footage looked like an awesome space shooter. Too bad it was Japanese-only release.