The Dreamcast was an amazing machine.
The top notch fighting game selection hasn't been seen on another console since. Powerstone, Powerstone 2, Marvel vs Capcom 2, Street Fighter III, Street Fighter Alpha 3 ... this damn thing was a Capcom stomping ground.
Can't forget classics like Soul Calibur and SNK vs Capcom 2.
Sports ... back in 1999, Sega cut loose NFL2K. This dominated all NFL games at the time. There was no denying that this title was an inspiration for EA's first Madden attempt for the PS2.
Anyone remember Virtual Tennis?
Puzzle games were to be found too ... Bomberman was spectacular (especially with the Sega NetPlay) along with the many variations of Tetris.
Action titles like Resident Evil and Shenmue ... even the insane action of Crazy Taxi.
Factor in the "self booting", downloadable games ... this system was a beast. This is coming from the guy with every freaking console ... every game ever made though 2001. Trust me on this, get a Dreamcast and have at it.