In semi-chronological order…
Star Raiders (Atari 800) - it’s space, in 3D, on a cartridge! Still a great game.
Zybex (Atari XE) - really nice looking 8-bit shooter. 'nuff said.
Myth (Commodore 64) - ultra-slick animation and visuals, fun (if stiff) gameplay.
Dungeon Master (Atari ST) - atmospheric as hell. At the time, it felt like I lived in that damn dungeon.
Prince of Persia (Atari ST) - awesome animation, enthralling gameplay.
Wing Commander II (PC) - millions of rotating sprites, all coming RIGHT AT ME!
Doom (PC) - like Catacomb: The Abyss, but really really good looking.
Strike Commander (PC) - I used to just fly that damn plane around, in awe of the visuals.
Toshinden (PSOne) - at the time, this thing just blew me away. The big-screen showing the fight was just amazing. Crappy animation though.
Castlevania: SOTN (PSOne) - such design, such style. Ultimate 2D game.
Metal Gear Solid (PSOne) - Well, yeah.
ICO (PS2) - most. beautiful. game. evar!!@!
Splinter Cell (X-Box) - about time we started to get good lighting in games. The E3 demo blew me away.
(note, I did not include any arcade games. Not 'cause they didn’t blow me away, but because I always accepcted the fact that the arcades would rock on anything I had at home)