Catherine
Why it was overlooked: Niche sexy Atlus game.
Why you should play it: Catherine is just one of those games that blends many genres together in a way that makes it virtually impossible to sound appealing when describing it. But when you actually try it out, you find yourself in a crazy action/puzzle/sim/thing that is as tense as it is addictive. Definitely not for everyone since it's a major departure from, well, anything! I'd put it in the same category as Killer 7 in the sense that it's literally nothing like anything you've played before it.
I want to believe you, I really do. But urgh... you're right when you said it is impossible to sound appealing when describing it.