The Grandia series of course!
People know of it.
People even really like it.
Yet it still fails to sell truck loads eventhough its one of the most solid and enjoyable RPG series out there!
Also the Dreamcast! (i know its not a game but it was still HUGELY under-rated!)
The Dreamcast had so many brilliant and classic games (many of which are still being played today due to the HUGE amounts of Dreamcast to gamecube/ps2 ports) and was a pionier in networked games consoles being the first home games console to truly bring the online gaming experience to the average home!