First WOW, was an old ElectroMechanical gun game called Ninja Gun.
Next probably was Sinistar. The graphics were great, great gameplay, and the Sinistar yelling at you (scaring the crap out of you), was just awesome.
Dragons Lair, Astron Belt, and Cliff Hanger. All stood out as amazing when compared to most all the other games of the day. Not so in gameplay, but in looks and sounds, by miles.
Next was probably Outrun. The best driving game Id ever seen, or played. Great shading, beautiful colors. Excellent background music, great speed and challenge, and a hardcore shaker wheel with an inch of violent travel. Perfection.
Somewhere around this time, I found Continental Circus 3D. The game doesnt seem 'all-that' in 2d, but see it in 3D, and it will blow your mind!

The entire thing is deep into the screen, and very often cars smoke, and
wreck.. and parts and tires fly out of the screen at you. Awesome!
Afterburner II - Motion cockpit. Awesome rockin guitar soundtrack. great graphics / shading. Fast & fun.
Hard Drivin was also a huge WoW moment. The graphics were pretty basic, but the controls and physics were so realistic, it completely made the experience so much more than anything else. Even modern racers pale in comparison.
Virtua Racer - First 3d racer that looked decent. Good play and sounds.
Cool race cam monitor for spectators to watch.
Fighters were good fun (Killer Instinct is still my fav fighter to play), but they never gave me a wow feeling... Until, Tekken 3. That was the first game which looked good, sounded amazing, but most importantly, had some of the most realistic martial arts moves (especially use of some little-seen styles/moves).
It was one of the few games that actually used motion capture from excellent martial artists... and it shows in the characters nearly perfectly replicated movements. That sadly cant be said for the next Tekken, nor most all other 3d fighters... which have really awful and unrealistic animations.
Black Knight 2000 (Pinball). Love at first play. Hearing a Choir of singers on a pin was a jaw dropper. Fast, insanely awesome soundtrack, great look & theme. great voice work. highly addictive.
Honorable Mentions:
(Oooohs and Ahhhs, but not quite WOWs?)
Marble Madness. Amazing pre-rendered graphics with excellent contrast. Awesome stereo sound, with wildly unusual, luscious-synth score. Great atmospheric game, a real playable work of art.
(If only it would have been longer, and faster ... )
MK1 - love the photographic digitization... but the res was too low, and a bit too limited of gameplay, as well as what seems like too much 'cheap-ness'.
T2 - Love the kickback guns. great play. good sounds. fun.
Ridge Racer - Awesome Drifting gameplay. Some Nice pumpin soundtracks.
Daytona USA - One of the better looking 3d games, excellent play. More realistic and challenging, than all the other racers. Similar to hard drivin in its realism. Too bad the sequels didnt follow that path.