Kotor.

I had a ton of fun 100%ing Super Mario Odyssey. There's a big amount of post-game content and a good amount of variety in exploring the different levels. Some of the moons need a guide though since they can be reallt vague.

I don't think I've ever 100% a game. I don't care about achievements and I've finished the campaign/story on many but I rarely go back to any.

Why? The padding is there for those with the stomach for it, but you can just… play a new game once you’ve stopped having fun?

I burned myself out of many a game as a kid attempting (and usually succeeding at) 100% them, so I learned my lesson. Nowadays I just play for fun and maybe go after the platinum if I liked the game enough. My time has value and I'm not going to squander it to "look at the minimap, go to waypoint/marked location, collect random collectible, rinse and repeat for 10-15 hours", nor am I spending dozens of hours grinding some random activity.

For example, I did almost 100% all Yakuza Kiwami. Did all side quests and enjoyed most of the random activities! Iirc those I had most trouble with were karaoke and billiards, but I still had tons of fun learning them and gradually getting better at them. But fuck me I'm NOT going to grind the coliseum for hours just to buy random weapons that I don't need but are arbitrarily required for the 100% completion.

I've also learned not to rush it. I frequently replay games that I like, so if I miss an achievement, that's fine. Maybe in five years I'll pick the game up again and grab the random achievement I missed the first time around. There's no need to sweat it, no need to read guides before/while playing the game and potentially spoiling me some major story events, and no need to immediately replay the game just to reach that random achievement.

That being said, the game I had the most fun with was CrossCode. Movement is fluid, combat is snappy, story and characters are fun and puzzles are actually challenging. It's the most charming experience I've ever had playing a game, and it's why it immediately jumped straight into my top favourite games ever. There is technically a "completionist list" within the game with some abdurd and missable requests, but it's not required to 100% the game and it's basically just a pile of challenges that you can tackle on if you feel like it. If you don't, you can just play the story, do the side quests and collect all the treasures, which is a lot of fun. The platinum only requires you to beat the story iirc, so you don't even need to do any of that; I did it because I liked the game and wanted to do it. Twice! I bought the game on PC and console and 100% it both times.

Most other games that I enjoy completing are platformers/collect-a-thons, such as Spyro, Crash (except Crash 1, never managed to finish it, but had tons of fun nevertheless), Ori, Celeste, PS1 Oddworld games, etc... and metroidvanias, if they are not overly long (basically every one I've played except for Hollow Knight).

The longest run I had was Final Fantasy XIII. I liked the game so much that I kept going back to it over the years, slowly chipping at the side content and grinding my way to max level. I got the platinum almost ten years after starting my save file, and I wouldn't have enjoyed it nearly as much if I attempted to rush it all in one sitting.

I've 100% Kingdom Come: Deliverance three times back to back if that tells you anything. Red Dead Redemption 2 is also up there.

Most Lego games. It's like a physical pain to me, NOT to 100 % them.

Little Kitty Big City, the superior cat game

Two games I have platinumed on PS4 that I still go back and play are Subnautica and Kerbal Space Program. Not sure if you mean 100% as in like scan and collect every item, or get all the trophies, cause I don't think I've ever 100% a game in that way.

Kirby nightmare in Dreamland

I got 100% on Final Fantasy X-II. Don't. Just don't.

I've 100 percented a few games without getting tired of it. In fact, some of them only just began with my 100 percenting.

Factorio Pacific Drive Learn to Fly 3

I typically don't try for 100 percent.

Subnautica. It's not long but I enjoyed every minute of it. And the requirements for a 'perfect game' on steam aren't too difficult.

We didn't 100% yet, but we did just beat Super Mario Wonder. It's a lot of fun if you like the side scrollers.

City Skylines

Umineko VN.

It has about 100+ playtime and excellent story. The anime sucks ass though.