Virtua Cop. It was the first 3D lightgun game (As far as I'm aware), and that aside, it provided me with a horrific amount of gameplay. I mean ok, you can't complete with the Seeburg Ray-O-Lite, but nonetheless it was pretty groundbreaking. A strong case for my getting a Saturn.

I can't wait for Omicron 2. The first one was awesome enough, if flawed. 2 has a chance to be one of the biggest games out there.

Jumping flash! First 3D platformer I ever played, and to this day one of the best.

Poy-poy. Like many party games it has a simple premise (In this case you throw heavy/sharp/explosive things at your opponents until only one is left standing.), and this is executed with something better than most other offerings have short of SSBM.