I think the Turbo Grafx-16 is one of the most unappreciated consoles ever released. It had some great exclusives...Splatterhouse, Legendary Axe, Bonk, Ninja Spirit, Blazing Lazers, Devils Crush and Military Madness among many others. It was also the first system that allowed you to play the same games on the go via the Turbo Express. Add in the Turbo-CD with some more great games...Y’s Book 1 & 2, Valis 2 & 3, Lords of Thunder and you have a system that really was ahead of its time. I just wish more people had a chance to enjoy this great system. 

The Apple Pippin...

Speaking of the Saturn, I would have to concur with others here that it qualifies as underrated.

It had some really awesome games; Panzer Dragoon 1 and 2, Nights into Dreams, Radiant Silvergun, Saturn Bomberman, Exhumed/Powerslave.

Yet due to its poor sales, particularly in the West, it has been largely forgotten.