Metroid--the very first NES game I ever played--it allowed me to walk 'backward' that was the future right there.
R-Type on the TG-16, the graphics amazed me (and the game is not bad)
Ghouls N' Ghost on the Genesis, again the graphics and the sound as well! Obviously great game and all (many early Genesis games could fill that spot).
Then the first CD game I saw
y's book 1 & 2 on my friens Duo! Amazing intro, again I was seeing the future!
F-zero on the SNES, smoooooth pseudo mode7 3D I still love this game!
Batman Returns driving levels on the Sega CD--blew me away, and I loved to play them... the game would have been a total distaster if they did not put an option to play only the driving, one of the few "true" Sega CD titles, one can only dream of a Sega that did not chase after the full motion video so much...
Silpheed on the Sega CD--what an audio visual threat!
The Need for Speed on the 3DO, this game was so far ahead of anything available home at the time!
Sega Rally in the arcade (the list could be filled with 80s and early 90s arcade games).
Doom on a 486 DX2 66, amazing 3D and sound track, it just blew my mind back then!
Quake on some Pentium machine, that was just astonishing (even before 3dfx cards)... The discovery of LAN multiplayer! It killed my exam scores un school! and full 3d!
Wipeout on the PS1, so smooth and the sound track was just amazing!
Soul Calibur 2 on the Dreamcast (many DC games).. visual tour de force, extremely smooth gameplay and animation.
God of war 3, uncharted 2 & 3 on the PS3, these games made me fall in love with hardcore gaming again--That God of War 3 intro "level" I guess!
Axiom Verge (with headphones or a very good sound system) I love the ambiance and the sound just blew me away. Only one man's work and passion was poured in this project!
Killzone:SF on PS4, it showed what potential this gen had (and was at times just genius in its level design, I wonder how it would have turned out it pushed
back months, as I feel the last third of the game was not polished).
Many more... I just got Forza horizon 4 on PC and I must admit it's great!