Got a few more:

Sonic the Hedgehog CD: This game was probably the only game that did 2D platforming right. Take cool, large, chageable level design, add a metric ton of these huge ass levels, add fast speed plus the time travel element, the coolest secret level design I'd ever seen, and gameplay that's challenging as hell to play. I think we got a winner here, people.

Phantasy Star II: One part epic story, one part simple yet challenging RPG elements, one part cool characters, and five parts dungeons and monster battles that are... dare say it... hard? Yes, we have an RPG that's actually hard, people. There is no excuse for you to not play this game. In fact, I encourage everybody with an emulator to download and play it. Its a game so hard it took me ten years... yes ten years, to actually beat.