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.

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

Undertale, for me. I have 0 problems with the game. Art style is great. Controls are great. Story is likely the most compelling I personally have seen. Not to mention the very appropriate humour.

I was going to say Outer Wilds but somebody beat me to it, so I'll say Final Fantasy 6 instead.

The Pixel remaster on mobile and Switch is a great version but it's missing the bonus content from the GBA release.

Fallout: New Vegas. Wait now, don't laugh at me. I'm painfully aware it was built on an engine that just does not cooperate and crashes regularly. BUT, the gameplay itself, the roleplaying, the fights (yes I do like VATS), and the choices by god the choices. So many choices with so many consequences, telltale wishes they were this cool. The only thing for me that's holding this game back is 1) the rickety engine it's attempting to balance on, and 2) unfinished quest lines. The devs for this game had so many brilliant ideas that never made it on screen, I don't know if they shot themselves in the foot, or if the deadlines were unrealistic. Even though some of the main quests between the warring factions feel lopsided, and some interesting things seem to go to a dead-end, the game never felt unfinished to me. There was so much to do and try, I never felt cheated by the game in narrative. Instead, I just want more because it was awesome how interactive the world was. It responded to my decisions and made a unique playthrough because of my decisions, I don't believe the predecessors even come close to this. Sure 3 and 4 kept similar mechanics, but the game didn't react to your choices. If I had one wish it would be to see Fallout New Vegas as the devs intended, with every plot line completed and polished, I'd even continue to play it on its rickety system. Though this would need to be a magical wish because there's no way that engine could handle the work needed, and converting this content to a new engine would be very expensive (so I'm told). I know she's not perfect, but goddamn she has the potential to be.

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.

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..

Outer Wilds

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

Outer Wilds

It's always Outer Wilds

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

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.

To The Moon

Firstly, it's fairly short, which I appreciate in a game that's primarily story-driven. Secondly, the story is damn near perfect. When I got to the reveal towards the end I actually sobbed (quietly, in a manly way). No other game has ever affected me that way.