I'll limit my choice to games that made me *instantly* go "wow", not after a while of playing them. Naturally, this is mostly achieved by technical fx and eye candy...
All Amiga, of course
Flashback - the animations. And the gun sounds.
Super Stardust - Rendered asteroids. And the tunnels, of course!
Pinball Illusions - Multiball, anyone?
Brian the Lion - I really liked the zoom effect