Guild Wars, especially for the PvP mode. I loved the visual feeling of the game, it felt sharper and less cartoony than a WoW.

Some classes were kind of novel too at the time.

And the feature I loved was the limited skillset you had to chose : you could be lvl 20 (max) and know 30 spells but you could only pick 5 in your active bar. It made for so many interesting builds and combinations !

Lots of contenders for me: Resident Evil 2, A Link to the Past, Ocarina of time, Goldeneye, Half-Life, Diablo II, Skyrim, Alien: Isolation, Borderlands 2, Mario 64

But I gotta go with Runescape

My vote goes to Shadow of the Colossus. The story, the mood, those damn creatures. Just enough frustration to keep you going and enough variation to not make it boring.

If we're going really old school, then Space Invaders. Its way of leveraging the hardware at the time to make the enemies and music speed up after you defeat more of them is elegant. Back then, the more things a game had on screen, the slower it ran. So, destroying more enemies removes more things from the screen, causing both enemies and music to speed up.

This is something that's taken for granted today, but I think at the time, it was genius.

Metroid Prime has to be pretty far up there. It was a bold step forward for an established franchise that could have gone wrong so many different ways, but holy cow they nailed it. The controls are probably the only weak part, but to be fair dual analog controls hadn't really caught on yet. Every area of the map has character. So many of the boss fights are memorable, from Omega Pirate being fueled by raw Phazon and destroying its own soldiers, to Thardus whiting out the whole arena, to Meta Ridley wrecking the shit out of the Artifact Temple. The music is great, bringing back bangers from previous games, subtly remixing in other motifs from the past as well to give the game a familiar feeling, while adding beautiful new ambient music of it's own. The plot progresses forward with only a limited amount of cut scenes and dialog. It combined two genres in an innovative new way that 20+ years later still hasn't really been recreated yet.

And then once you've finished playing everything and finding every last thing as intended, there's still more fun to be had in learning some of the more basic glitches to get items way earlier than intended. Giving the devs the middle finger by getting items the first time around without taking a long backtracking trip later to come back and get it. Speeding through areas and blasting through boss fights with equipment and weapons you're not supposed to have yet. It contributed in large part to the birth of the modern speedrunning scene as people came up with more and more creative ways to get around formerly impassable obstacles.

20+ years old now, and it still holds up (as long as you play Primehack or Remastered to get more modern controls).

In very recent times, I honestly believe Zelda:TotK is very close to being perfect.

Majora's Mask was it for me. You replay the same areas over and over, but the game never felt stale. Tons of great mechanics and challenging dungeons that were totally unique from OoT. Having the story be told out of order was really unique and creative. Plus being able to fight the final boss as many times as you needed (on easy or hard mode) was nice.

Witcher 3. They very well combined open world with story telling, with tons of side quests, many of which affect the story. The characters aren't one dimensional. For example Bloody Barron is a low life, but also draws sympathy as he pays for his sins from the past. The world is also unforgiving, many times you have to make a decision between shitty option and even shit tier option. The graphics and characters are also very detailed. All of that creates a great atmosphere.

If you haven't played it, you should give it a try.

I have always been a fan of stealth games. Dishonored (especially the first) scratched the itch perfectly! It's atmospheric. It's not open world, but each level has its own area to explore that is filled to the brim with stories, sometimes a small side quest etc. I also love how you get to influence the ending.

Celeste has just perfect controls and pacing. I still think about it. I wasn't as touched by the story as others but many were. I'm still playing Super Mario World and find it so impressive and charming.

Bioshock I think, loved it so much. Excellent writing and graphic design. Wish the remaster had improved the visuals more tho

A big one for me is Fallout 1. I only played it for the first time a few years ago and it is one of the only games where as soon as I finished it I wanted to start it again. The only reason I didn't was to play Fallout 2. There is an extremely valid argument that Fallout 2 is better, but the pacing of 1 is so good. It opened up a whole (niche) genre of games I thought I didn't like, isometric crpgs, especially ones with turn based combat, relatively low player power, and serious consequences.

The other game I could replay over and over again was Metal Gear Solid 1. In my opinion it is the best in the series relative to its time of release, if that makes sense.

Also obviously Halo CE.

Outer Wilds

Dragon Age. I literally fell in love with Alistair while studying for my masters, so it must have been an excellent storyline for an RPG. I also played it through in full twice because it turned out my initial character choice made my perfect ending impossible..

Super Mario RPG for SNES. ... I'm old

Hollow knight. The gameplay, the smoothness of the controls, but also the universe, the atmosphere, the fantastic music. Absolutely wonderful game.

Perfection is overrated. Most of my favorite gaming experiences are with games of which I would be able to cite plenty of flaws.

I like games with sharp edges.

That said, there are a lot of good games being mentioned in these comments.