Second Sight was under-appreciated? I remember when it came out it got solid reviews (IGN 7.9, Edge 7/10, GameSpy 4/5, Game Informer 8.5/10). I mean It's a good game, not amazing, and I think it's remembered as such. And @zkowaliczko1994, Metro? A series that was fairly well received and sold well enough to get a sequel and a re-release, all within the past five years, is hardly under-appreciated.
As @bisonhero mentioned, Driver: San Francisco is a better example. UbiSoft said it sold well, but it never seemed like a popular game ... and after some terrible entries in the series it's no surprise.
It might sound crazy but Duck Amuck on the DS stands out to me. I remember the devs saying it's the only DS game that got approval to disable the sleep mode but there's a mini-game where you had to close the console. It was super short but the way you interacted with Daffy as he broke the fourth wall... I mean it's not a classic, but it was inventive if nothing else.