Only gaming-related accomplishment that I'd care about (other than being involved in games' creation or preservation).

Congrats good sir. Been using Linux for almost as long as you (switched around 2009-2010, kept a Windows box around only for gaming) and only recently started getting my feet wet with Wine. I hope to someday be at your level.

Making a dent in my backlog! Of the mere 200 or so games I bought last year, I managed to complete a whopping two of them! ...oh, waiit!

Gaming wise, maybe 100%'ing GTA Vice City without using cheats, although I did use a guide to understand in what sequence to perform missions and the optional activities.

It’s not about "smartness" but about experience, everyone can reach that given enough time. In addition WINE is much more powerful today than it was at the time (the 1.0 release was not even out yet), and, I think, easier to learn.

So what took me many years would probably take you much less time, especially as, if I remember correctly, you already have a background in software engineering (I had none at the time).

That is genuinely impressive. I played the GTAs a lot, but I never had any illusions about being able to find all the stunt jumps and hidden packages, much less without using a guide. In a similar sort of game, I believe I was at 99% completion in Saints Row 3 or 4. There was maybe one lone collectible somewhere out there that I just couldn't find..

And my backlog isn't going anywhere fast. January last year was productive, with a few short (and excellent games) finished, then I went on to mostly play 100 hour RPGs for the rest of the year. A lot of gaming, but few completions.

Imo, putting in the time makes achievements all the more respectable. You don't control or earn how much natural giftedness you are born with, but you do control and earn the time and energy you dedicate to become good at something.

In my case, I failed to recognize the importance (from the perspective of enjoying my game collection in the long run) of more fully controlling the environment I play games in starting with the OS while I had more time 10-15 years ago (with a career sure, but unmarried and without kids), so now I have to play catchup while I have significantly less time.

I did invest a lot of time in other technical endeavors that are now paying their return on investment, but not this.

But thankfully, like you said, the tooling have matured quite a bit since you've done the undertaking so that's less work for people like me playing catchup now.

Of the three GTA3 games, I'd reckon Vice City is probably the easiest one to 100%, although I'm not gonna lie, I was having heart palpitations during the last couple of levels of the paramedic mission. The smaller map size and much easier timed checkpoint side-missions compared to GTA III and San Andreas also helped. I never came close to beating them in GTA III and I also used a cheat to beat GTA III's paramedic mission. GTA III also taught me the important lesson of using a guide as I was a fair way into the main missions before I discovered that there were perks such as infinite running if one completed the paramedic side-mission, and that mission was easiest to complete before getting too far with the story missions, so I had to restart the game from scratch.

However, in the case of GTA Vice City, where I was aware there were some game-breaking bugs at least as far as preventing 100% completion, I followed the guide to the letter but I can't help feeling that this spoilt the game by turning it from a free roaming open world experience into effectively a linear game for me.

In the case of San Andreas, which I'm busy playing now and have just unlocked the third and final city, I decided to focus less on 100%'ing it and more on playing it in the spirit of an open world and then just using the guide to see I'm on the right track every now and then. I've still tried to complete most missions though, especially one's which give one additional perks rather than just being an achievement. Similar to when you were on 99% completion in SR, I had collected 49 of 50 snapshots and must have used a guide 3 times to try to figure out which one I'd missed but to no avail. I eventually found a website where you could upload your save file and it would then be able to tell you exactly which collectible you'd missed... and the one I was missing was one I'd would have sworn I couldn't have missed... and yet I had.

Of the three, San Andreas is hands-down the best... so far. Hope it ends well.

...and I'm too scared to start a 100 hour RPG right now. That takes dedication & time! I still need to complete Icewind Dale which isn't exactly a long RPG, but I got side-tracked a couple of years ago and I'm not sure I'll even remember how to play it when I eventually get back to it :(

I'm not a good enough gamer to have accomplishments that would mean much to others, but that doesn't mean they're meaningless to me. ;) Here's a few I can think of, mostly from consoles and mostly older ones at that...

Super Mario World, SNES - This is probably the game that I have been the best at. I don't have a specific time or anything, but I have very little trouble starting from scratch and getting every exit from every level.

Metroid Prime, GameCube - This may be my favorite game of all time. My own best times are nothing compared to the best speedrunners out there, but this is another game I know very well, and due to the fact that I have the original release version, I can do most of the tricks that were nerfed in later rereleases of the game. Every so often I go back and try to beat my own best time, and after one or two playthroughs I usually manage to shave another minute or two off of it.

Godzilla Destroy All Monsters Melee, GameCube - Okay, this one isn't an accomplishment per se, just one of my favorite gaming memories ever. There's a cheat that allows you to pick up nearly any object in the game, and some of the objects have very weird physics since they weren't really intended to be picked up. One time I was playing a multiplayer match against my best friend with this cheat enabled, and we each picked up a freeze tank at the same time. We threw them at each other simultaneously, and they collided in midair. One of them was deflected straight down at the ground. The other shot into the sky at high speed and disappeared, which was funny enough on its own to us, but then almost a minute later it came crashing back to Earth and flattened my buddy's monster, doing enough damage to KO him and leave me as the winner. It was so unexpected and we both cracked up and started laughing so hard we could barely breathe. We have tried to recreate this many times, but have never managed it successfully.

I'm very much in the same boat. I'm not an achievement hunter, I've usually zero interest in 100%-ing a game or overcoming self-imposed arbitrary challenges (like, say, finishing Doom with punches only - I'm sure there's someone out there who made it!). That said, I'll always be proud of completing Antichamber, which I think is a truly great game, regrettably not on GOG.
The only comparable experience, for sense of accomplishment, would be finishing Metal Mutant on the Amiga (but also Space Crusade - and X-Out on the C64).
(Other feats likely don't matter much, like reaching the 100th level in Defender on the Atari 2600, or finishing Punkiller on the very first try...) True. I managed it with Machinarium.

Aside from beating few older games on highest difficulty, probably reaching top 100 in FFXIV ranked PvP several seasons and being constantly matched with pro players back during early Dota 2.

Despite enjoying the competition and challenge, I play a lot of other games more casually.

In Bloodstained: Ritual of the Night, I've been able to clear most of the game (except for the first boss, where I cheated, and the endgame, which I haven't played but which isn't as hard as the early game) on Nightmare (not New Game +).

By the way, specking of feats, one of the greatest feats (or most terrible feats, depending on who you ask) is the Pathfinder 1e feat Sacred Geometry. It allows your character to apply metamagic feats for free, except that you, the player, have to solve a math problem. (I think I would be able to solve the problem without bogging down the game; other players, however, might not be.)

Beating The Legend of Zelda: a link to the past.
After about ten years. I started it when I was a kid, got lost, didn't know how to progress and just moved on. Years later I got a snes mini and finally beat the entire game. It felt pretty magical.

Ten Years? It took me a few days. Or weeks. Can't remember, it was so long ago. That game is so great I couldn't stop playing.

100 percenting SpongeBob Squarepants Super Sponge on PS1

Reaching 1.000.000 points in Munchman (a PacMan clone on a TI-99/4A home computer).

I was expecting something fabulous to happen, but no, the score counter just went back to 000.000, after reaching 999.999.

It took many hours to reach that, I don't recall for sure but could be 8 hours. Luckily the game had a pause function and/or a new level didn't start until you moved (if I recall correctly), so I could take short pauses to go to toilet and maybe eat something, but only short pauses as I was very concentrated on the game.

I don't think I played the game at all after that feat, it lost its meaning to me.

Frankly, I don't think it was that hard to reach 1.000.000 points if you were any good at the game, as it kept giving you extra lives quite often, so dying every now and then didn't really matter that much. It mainly took persistence more than extraordinary skills, I guess.

Come to think of it, some other TI games had a similar problem. "Parsec" also became too easy in the long run because the game just kept pushing new lives (ships) to you after certain amount of extra points, and also the games stopped getting harder after awhile.

One exception was TI Invaders (a Space Invaders clone), it never became too easy, it just became so hard at advanced levels, plus the whole game would end altogether if the enemies reached the bottom of the screen, no matter how many ships you had left. I recall I could never get past the levels where there started to be more and more blinking aliens which couldn't be hit if they blinked off. It frankly became a matter of luck whether you would hit them or not...

I recently beat Castlevania 3 legitimately, without save states. It's probably one of the toughest games I've beaten, but it's such a great game it never felt like a chore. I just wanted to keep playing until I perfected it. The game is pure quality - an all-time classic.

I have previously beaten C1 properly, in one sitting. I guess I just feel at home in a haunted castle, with a whip in my hand ;-)