Megamix is a terriable game one of the worst fighters ever. The only decent thing about the Saturn well about any Sega console is that they do damn fine arcade ports. 2D games on the Saturn look fucking awesome epcially the 2D fighters. SNK and Capcom released basically all thier fighters on the Saturn. Its too bad Castlevania: SotN never got a US/EU release on the Saturn.
Treasure who released Gunstar Heros (FUCK YEAH!) on the Mega Drive/Genesis also released some pretty awesome Saturn games most of witch only got an Japan release.
Radiant Silvergun is a great 2D shooter but you'll need to import it.
Silhouette Mirage never played it but its an Treasure game for fuck sake. also needs importing.
Guardian Heroes is also a great 2D beat em up.
Working Designs (remember Lunar on the Sega CD anyone?) also localised alot of RPG's onto the Saturn too, Dragon Force is probably the best one.
Nights is good if you like Sonic Team doing alot of acid and then vomiting a game onto a compact disk.
Sonic Jam if only for the bonus songs and movies you could watch on it.
Panzer Dragoon 2 great on-rails shooter.
Panzer Dragoon Saga, Now I have never played this but it's ultra rare and apparently one of the best RPG's ever made.
Bomberman and Loaded, yes yes yes!
Astal, another Saturn game I havent played that is apparently really good too.
The Virtua series of games probably Virtua Fighter 2 and Virtua On are the best.
Resident Evil 1, In my opinion the Saturn version looks just a bit more refined than its Sony companion.