The first Bioshock is very high on my list, as well as Half-Life 2, but those may be a bit cliche. I think more recently and perhaps more "game" like would be The Binding Of Isaac. It's a perfect game to me. Infinite playability, a veiled plot that requires some thought without invading the gameplay, awesome boss-fights-done-right in a day and age when people think boss fights are a dated concept. It's everything I could hope for and much much more, with more content CONSTANTLY being added.