There are some real quirky titles on the Dreamcast that I love to play.
Both Areowings are great flight simulators (if a bit limited)
Super Runabout (You can race a tank!)
Omikron (Freaking David Bowie, dude)
Stupid Invaders (Old fashion point and click a la Sam and Max)
Ooga Booga (Wacked out multiplayer)
Starlancer (pretty good PC port)
Speed Devils (actually a good racier with a gambling element)
Jet Grind Radio (just get it...no questions asked)
Of course there are the obligatory RPG's (Skies, Shenmue, Evolution, Seventh Cross), fighters (Plasma Sword, Power Stone, Street Fighter, Soul Caliber) both Sonic titles, the 2K sports are good for their time. Capcom gave the system a lot of love.