Definitely this. I remember it being the first game where character models and animations were starting to get very close to looking like theatrical CG animated movies. Even DOOM 3 from a year before seemed far off from that. Not to mention the physics.

Donkey Kong Country trilogy and SMRPG for the Snes.

Doom 3

Splinter Cell (don't remember which one) that was on og xbox

Hydrophobia. Most games can't even beat that water today.

Metal Gear Solid 2 and Crysis. I might also have to say the first Metal Gear Solid, but I had too little experience back then to be able to really say. I think I've also got to agree with posts mentioning Half-Life 2 here.

Power Ranger on Game Gear, truly a 16 bits game running on a portable 8 bits, this is my WR here:

https://www.youtube.com/watch?v=RpzsD5mdprk

God of war 3 blewwwww my mind. Still looks great on PS3.

Games that come to mind for each generation:

Gen. 3: Super Mario Bros 3.  It was on the same console as Mario 1, but it looked so much better.  It looked next gen.
Gen. 4: Donkey Kong Country games.  I personally was never into this series, but I thought it looked great next to most early PS1 games and it was supposed to be a generation behind.

Gen5: Final Fantasy 7.  The FMV and the hand rendered backgrounds made this game look amazing.  They really leveraged all of that extra storage space on the CD ROM to make a game that looked amazing compared to anything that came before.  Sure, Cloud on the overworld map was a blocky mess, but that made everything else in the game look better in comparision.  Kind of like a mole on a super model's face.

Gen 6: Final Fantasy X.  The cutscenes on this game look amazing even today.
Gen 7: Final Fantasy XIII.  For all of it's flaws, graphics were definitely not one of them.  The game looks better than anything else on the PS3 and it came out fairly early to mid in it's life cycle.  Most PS3 games look dark and drab.  FF13 has bright cheerful visuals that really show off how great the graphics are.

Gen 8: Final Fantasy 7 Remake.  I still haven't played this game, but I am impressed by the visuals on the characters interacting.  Most PS4 games have a serious Uncanny Valley problem, but FF7 seems like they have overcome it.

And the game that takes the all time prize:  Dragon's Lair.  Game looked like a Disney cartoon while other arcade games at the time were things like Donkey Kong and Ms Pac Man.  Graphically it was decades ahead of it's time.

Yeah there was nothing else like it at the time and the following years. Source engine is so good and scalable. Its still used in some modern games today today like Overwatch, CS:go and Half Life: Alyx. The Havok physics was also insane. I remember upgrading my GPU with the 7800GT to play the game and was totally mind blowing then.

Crysis

Even against it's new remaster, there as aspects of the original that still look better than the remaster. The original was the first time my eyes had an orgasm even if the fps was terrible on my computer back then.

Flight Sim is 2020's version of Crysis from what I have seen though