Still Quake.

Great atmosphere, and degree of simplicity while still quite challenging.
I cut my chops as a gamer with Quake, so of course there is nostalgia, but it is also about what ID got right ... so right it made me desire to be a gamer.

Things like key macros, using bots and developing levels myself as well as playing levels (even episodes) developed by others, competing with friends etc. I got in deep and got it so bad, I still feel the pull and attraction decades later.

NOLF, for its gameplay, design (graphic-wise, level-wise), plot, settings, characters, dialogues, themes and music. Mostly.

But Fallout (1/2) and Prince of Persia Sands of Time are close contenders. Total War (say, Medieval 2 for instance) is certainly up there with them.

Like Postal 2 ?

Mirror's Edge, easily.

It's an interesting choice being a sequel that has since been sequeled for want of a better word.

What exactly made that game your favourite?

I love games with different scales gameplay, for instance the Men of War series that you can play as a RTS or zoom in real close and have it become almost an action RPG where you just control one character or two in the field.

Total War games have great strategy-level gameplay and then the battles become awesome RTS. And I love their historical feel, they really immerse you in their respective eras and cultures, with the units and the landscapes. They involve diplomacy, economy, strategy, tactics and scientific research, but they are less overwhelmingly complex than Crusader Kings, and more detailed than Civilization. They just hit the right balance for me. And provide a great feel of the geopolitical stakes of their eras. Gorgeous graphics, gorgeous gameplay(s), infinite replayability. It's like a "total game", that encompasses many aspects that I usually tend to seek in separate games.

And maybe I'm marginally more interested in the diversity of cultures and technologies of "Medieval 2" than, say, "Rome" or "Empire". It's also a complete game, before the avalanche of DLCs that plagues the later releases. I love the franchise, but "Rome" and "Medieval 2" may be my favorite, thematically, with a slight advantage to the latter.

Yeah for me that was a huge selling point too.

I loved Medieval: Total War and its expansion Viking Invasion.

I bought Rome: Total War but didn't enjoy it so much as the macro strategy layer was broken.

I also bought Medieval 2: Total Wat and found it lacking somehow even though the strategy layer was probably better compared to the last one.

After that I stopped buying games in the series. I would love to play the original MTW but it is so badly progarmmed that it is pretty much unplayable on modern hardware it seems.

My favourite game of all time, i said several times, is Grim Fandango.

And if I can choose a second place of honor, Starcraft is probably the game that has stolen the most hours from me.

It was Ultima IV for the longest time. I played that before the internet became what it is with walkthru's, secrets and tips being posted everywhere. Figuring everything out in IV as you played felt epic and was incredibly fun, figuring out moongates, sailing into Buccaneers den for the first time, finding your groupmates, secret doors, the dungeon crawling and so on.
Alas, I got to the last question right before winning the quest and couldn't figure out the order of the 3 fragments and failed. You couldn't save in that dungeon and I didn't have it in me to go thru that marathon dungeon again to possibly fail once more so I never played it again.
I discovered GOG because of this game and it was my first purchase here but it never was the same and I've never gotten far the few times I've tried playing. It's always installed on every PC I've gotten though just in case I do get the urge to try again.

Since then and gaming for around 30 years now, having a favorite is temporary... hundreds of hours in Civ II, as well as other civ games, warcraft/starcraft/c&c, many of the might and magic's (rpg and tbs)... to present day, Witcher 3 is a masterpiece, x-coms past and present. And many more.

Tactical tbs games are what I've gravitated to in the time of covid so I assume the next great one I find that I can sink hours into will be my new favorite.

Civliization, the transition of humankind through history. In the first one you also got a global rail network and building the palace

Sacred 2 if only it ran better on Win 10. Unfortunately, the community patch doesn't really help either.

2nd place at the moment. Outward Definitive Edition and Mount & Blade Warband (Mods)

Sometimes it's hard to go back again... but there's always hope for a bit of that old spark. ;)

Yeah, I've played video games since the 70's and have had many games that I loved... at least for a time. But that's why I ask the question... it's interesting to see what people hold most "valuable" at any one time.

Quake 3 Arena, Far Cry, Rebel Galaxy.

I'm not familiar with the cat situation with Postal 2, but I really do mean absolutely everything involving cats (so long as the game isn't specifically about hunting down and viciously murdering cats.)

Examples of Runner Up games:

Cat Quest - player character and most NPCs are cats

Divine Divinity - There's NPC cats all over the game world just living their best cat life by going around chasing rats, rabbits, chickens and other prey. There's one cat that will follow you around plus an NPC cat that talks.

Gibbous - Kitteh

Yakuza 6: The Song of Life - Find all nineteen stay cats and take them to the Nyan Nyan Cafe, then you can take a break from whatever Yakuza is supposed to be about to do things like freed the cats and hang out with them because this is all that matters.
https://www.youtube.com/watch?v=CsuUSUsvRuE
https://www.gog.com/wishlist/games/yakuza_6_the_song_of_life

Vampire: The Masquerade - Bloodlines (PC).