Team Fortress Classic
I played it from release in 1999 till 2007 or so basically every day. I can’t tell you how many times I’d load it up before the sun went down and wouldn’t stop until it came back up without thinking anything of it. It’s still installed on my hard drive and I play it every now and then, though there aren’t really any good servers left. It’s actually the only online game I’ve ever really played (apart from a bit of HLDM and some beta builds of Counter-Strike).
The games listed below all stole many nights from me as well.
Diablo 2
Another mainstay on my hard drive since its release, and almost certainly my most played single player game of all time. It is just ridiculously entertaining, and incredibly immersive with its amazing soundtrack and artwork / graphical style.
Stalker: SoC & CoP
Janky, but probably the most immersive FPS games ever made. I make sure to play through both of them at least once a year, though I never could get into Clear Sky.
Fallout 1 and 2
I enjoyed New Vegas a lot, and I even enjoyed Fallout 3, but the first two are my favorites. Apart from being my favorite game world, they also have incredible soundtracks. Even when I put them up against the beautiful compositions in something like Witcher 3 I find that Mark Morgan’s work added more, or at least meant more to these games.
Vampire the Masquerade: Bloodlines
One of my favorite, and also one of my most disappointing games of all time. The super ultra mega fan patch 10.0 is nice and all, but it really doesn’t do much to fix the actual problems the game shipped with (like the fact that the engine is pure garbage, the levels are small and barren, the animation is a mess, et cetera). But even with those problems, I play through it every year because I love the game world and the characters so much. If Activision hadn’t fucked the release up so much maybe it would have sold enough to warrant a sequel.
Morrowind
My first open world RPG, and my absolute favorite up until I played Witcher 3. Having said that—and maybe it’s because I played Morrowind at a much earlier age—I was far more engrossed in the third Elder Scrolls game. After one botched attempt at a character, I hit my stride with the second and I just lived him for a year or so, trying to collect every decent item and complete every quest I could.
Oblivion didn’t do anything for me, and I didn’t even buy Skyrim until recently, and have yet to put much effort into it. What I’ve seen of Skyrim I’ve liked though, so it’s definitely something I want to get into.
Dwarf Fortress
If anybody ever tells you that you need great sound and graphics to be immersive, this is the game you point to. The night I downloaded it (back in the 2D build days when it was just starting to get press) I spent all night playing it. Then I spent the night after, and the night after doing the same. I got away from it after 40.xx came out, but whenever I play it again it always brings me in the way few other games do.
I don’t know if it’s age or what, but these days it’s extremely rare for me to find a game that just sinks its teeth into me and causes me to lose hours on end without realizing it like the games above did. With the hundreds of new games I have on Steam, Humble, et cetera, what games am I playing right now? X-Wing / TIE Fighter, and Age of Empires 1 and 2.