As far as labors of love go, Stardew Valley is probably the most current example. People paid for this thing years ago, but Concerned Ape keeps adding new features anyway. The retro graphics give this thing a timeless quality out of the box, so it already looks "dated" - this hasn't stopped the robust player community around it. We'll probably see this game stay relevant for a long time.
A videogame that was made with complete love and devotion to the medium, made with talent and sincerity, and is a pinnacle of everything it stands, something that will stand the test of time...
And nobody mentioned Stardew Valley? I spent too long looking for it and didn't find a single mention of it. Absolute mastery of its genre, an incredible amount of dedication spent by the developer listening to the fans, and I can't imagine it not still holding up 10 years from now, or even 20 years from now.
Baldur's Gate 3 is great, I love it, but there were so many performance issues with the game even with top tier hardware, and the game was borderline unplayable for others due to these issues. I have a little bias since my save didn't sync across devices with the steam cloud and I have to start all over. Love the game, but I just can't believe Stardew Valley isn't even mentioned.
Ocarina of Time. I'm biased because of nostalgia, but I genuinely think it's the best game ever created. It took everything that was great about the SNES classic A Link To the Past, brought it into 3D as an early N64 game, and improved literally everything. The atmosphere, the gameplay, the story, the time mechanic, the music... It's not perfect, in fact these days it's trivial to break many things in it with glitches, but I think it's absolutely the best.
Age of Empires 2, despite being Microsoft owned, is easily one of the best strategy games of all time and has very clearly stood the test of time. It's over 25 years old and people kept playing it a lot even before the HD remakes. I remember reading that the folks that made the 1st game often had to choose between "actual history or hollywood history" for some details, often going for hollywood because it made for a more fun experience.
I suspect Factorio might stand the test of time as well, and it's clearly something made by someone who really understands the medium. I haven't begun my factory yet.
World of Warcraft, at least for the first 3 expansions. I think the people that made it back then were utterly devoted to the story and gameplay, as were the players. I'll remember playing that until I die, so many memories.
The Persona series comes to mind. But probably more than anything Witcher 3, Skyrim, Disco Elysium, Stardew Valley, No Man’s Sky, Nier Replicant/Automata, Metal Gear Solid 3, there’s actually quite a few imo.
Mass Effect. I know some will disagree, the third game has a lot of glaring issues, and EA really fucked up the ending, but as far as a fully fleshed out story and universe with a multitude of unique and independently structured species, characters, and cultures I think it’s one of the best. The writing and possible story outcomes and decisions that vastly and permanently affect the story from the first to the third game are insane.
I feel like the labor of love part being something like Factorio, Satisfactory, NMS is fitting. Also grand scale, holds up well, graphics aren't the main point
Neither of these are popular enough to be on the scale of LoTR, but in terms of atmosphere and detail:
Hollow Knight - my absolute favorite thing about it is each NPC has its own voiced language recorded, babbling in the background as you read the dialogue.
Subnautica (the first one) - shitting myself with each new experience is something I'll always cherish. Highly recommend just playing without looking into the gameplay or plot. Has elements of exploring, resource gathering, base building, psychological horror (not graphic, just tense scenarios), sneaking.
Mass Effect. Even though it has its flaws, it was just an epic story, built up perfectly over three games. The ending is disappointing for some, but I really liked it. I was really excited for the sequels when the first one came out.
Final fantasy 6
Chrono trigger
Capcom vs SNK2
Soul Calibur 2
Super Mario Bros 3
These games all stand tall as giants of excellence decades after their release. Teams have already decent renowned executing at the peak of their genre with true craftsmanship and deep care into their design from mechanics to aesthetics to music to gameplay.
It's not a trilogy, but I gotta preach the good word of Ender Lilies: Quietus of the Knights. If you enjoy 2D metroidvania style games it's top notch.
The game just drips in atmosphere. The environments are beautifully drawn and designed, characters and enemies are animated well and the music just wraps everything up in a nice bow. It's a melancholy game and it literally made me cry at points and I'm not the type to tear up often when playing games.
The game can be challenging at times, but I wouldn't say significantly so. I would say Hollow Knight is more challenging than this game especially with some of the end game content that that game has.
The game is worth full price, but it goes on sale pretty regularly and probably is right now with the summer sale on Steam.
There's also a sequel out now called Ender Magnolia. I haven't played it yet but I will eventually.
Surprised no-one pitched Elite:Dangerous. Certainly a labour of love to begin with, incredibly talented sound design, first space sim to VR, truly devoted to the original material... Still going pretty strong (had a few weak years) with updates (only 2 DLC-ish major updates of which were paid) a decade later...
The Yakuza series I guess? Granted I've only played zero, kiwami and kiwami 2, but it all seems to be completely sincere in its craziness. It doesn't appear to pretend to be anything more than it is.
Semi-jokes aside, I am a bit sad that not a single person mentioned the first four Silent Hill games. The sheer influence that series had on video games as a whole, especially in the horror genre cannot be overstated. But I guess it is tricky with games because everyone has different tastes and interests. It is rare that games unite people the way lord of the rings did. Gaming is at once so broad and so niche.
Puzzle Pirates, frankly. Made by people who knew what they were doing, were extremely talented, independent, although eventually tried to hook onto Sega as publisher, almost killed the game and then re-purchased the game from Sega to continue as "re-indie" devs. Still going to this day with a stable player base of a few hundred. The game itself is very clearly hand-crafted and every one of the (few) developers left their mark on it. Feels completed and polished.
Final Fantasy XI. It's been online for over 20 years and still has a devoted player base. The game's scale is so epic that many people still haven't beaten the expansions.
When it came out it was so far beyond what we had seen in an MMO before - The only competitors were UO and Everquest, but the graphics, music, complexity, and storyline were miles beyond those games.
It's a game with unimaginable depth of play that takes years to master - not like the hand-holdy easy games we get nowadays. Truly a gem the likes of which we will never see again.
I have to ask, what spontaneously caused the internet to love the lord of the rings movies? For decades after they were made, only occasional jokes about unhinged 20 hour directors cut binges. Now? Frequent jokes about 20 hour directors cut binges, and endless sincere compliments. They’re good movies, to be sure, but the shift always seemed inorganic to me.
The first half of the description, combined with the unmentioned ambition of LotR, made me think of Star Citizen. But we'll have to wait another 5-10 years to find out if they manage to deliver on that ambition, and stand the test of time.