Uniracers(/Unirally) for SNES
I never met someone who knows this game. I think it is the best funracer which doesn't looks like Mario Kart.
dragon quest warrior: mosters didnt get anything like the attention of pokemon but such an awesome game.
does okami count? maybe not underrated, just underplayed.
Alan Wake. I didn't get as enough hype as I thought it would. It was a fantastic game throughout.
Superman 64.
Quest 64
The leveling system was unique for me at the time. The only thing that bothered me is that I wasn't able to save as I didn't own a rumble pack, so I had to keep the N64 on all day.
Divinity 2: Ego Draconis
It's a fantastic RPG that the reviews screwed any chance of success, for lame reasons.