Yu-Gi-Oh: The Falsebound Kingdom. It's a TBS game, with great graphics and an incredible story, but no one bought it because of the Yu-Gi-Oh label, and the fact that it was on the Gamecube.
Shadowrun (360). My friend introduced me to this one a year or two back, and I absolutely love it. The fact that it's multiplayer only was a bit off-putting, but it just doesn't get old
Legend of Zelda: Majora's Mask. This came out a year or two after Ocarina of Time, so everyone was still playing that, and the fact that you had to do everything in a short space of time pissed a lot of people off, but I think it was a cool gameplay feature. (That, and, I hated everyone in Termina and loved watching the moon crush them all)
Diddy Kong Racing. This came out for the N64 as well, but Mario Kart was a well selling kart racer, so nobody payed much attention to Diddy. If you've ever heard of Conker (i.e. Conker's Bad Fur Day - N64) Diddy Kong Racing was where he made his start
Crackdown. This was an older 360 game, but it was one of the first demos I downloaded when I got my 360, and I played it more than my actual games, so I went and bought it, and it was amazing. A lot of people think it's just a GTA rip off on steroids, but I think that the fact that you can jump over buildings and chuck cars everywhere was really entertaining
