I like this thread! Thanks.

I usually would harp on the benefits of turn-based in deeper systems, but I feel if we talk about strategy the OP really misses out on a subgenre that I recently very much enjoyed, and which is real time (although that might not matter as much): colony sims.

Dwarf Fortress is the granddaddy of colony sims and is probably the most complex game ever made. And it is for free, even though now a Steam version exists with some tileset graphics (the original has text) which costs a little because the creators had a health scare and decided they need some security. I think that price for the Steam version is fair as well. But this game has so many deeply integrated systems, that you can play endless. Or at least until the fortress is so big, has so many cats or socks to simulate, that even the most advanced computer goes into slowdown.

https://www.youtube.com/watch?v=VAhHkJQ3KgY

A lot of games are inspired by Dwarf Fortress and while usually simpler they often bring interesting new ideas to the mix: Odd Realm, Rimworld, Oxygen Not Included, Rise to Ruins, Against the Storm and so on. I am kinda addicted to that sub-genre, because just stripping out elements to simplify dwarf fortress leads to very different takes on what people deem important and then you also can add completely different ideas. So while Rise to Ruins and Rimworld are both descended from Dwarf Fortress they are actually playing very differently although I also can see all the similar elements. This subgenre is so inspiring and so wild currently, I very much enjoy it.

Yeah I've read theories that the Strategy community was very sizeable in the 90s/early 2000s, but the community didn't really grow much beyond that while the rest of the industry shot past it like a rocket lol. So while the community never left, it just pales in comparison to the rest of the games industry. Became a "dad" genre, which ironically is how I got into Strategy games

I definitely remember as a kid, Real-Time Strategy was always one of the biggest genres in gaming. Whether it was Age of Empires, StarCraft, Warcraft, Command & Conquer, Homeworld, Total Annihilation, Rise of Nations, Empire Earth, or even a Star Wars game called Galactic Battlegrounds, there were so many major RTS releases that would make headlines and are still recognizable names to this day. Hell, StarCraft literally became the sport of South Korea for well over a decade lol. 

But there's definitely other sub genres that take a ludicrous amount of time like you mentioned. If you're playing Civilization, pretty much any Paradox Interactive game, then you're going to be spending hours upon hours on a single game, and that's if you're well acquainted on how the game plays.

So there certainly will be certain sub-genres that will forever remain niche, but it is nice knowing that the genre still thrives in many ways, albeit primarily through certain franchises lol. Civilization VII is getting a full reveal next month and it will be on consoles day one, so I'm willing to bet it will bring down the skill ceiling to where it's as approachable as possible.

Unicorn Overlord is currently my GOTY, so I highly recommend!

Still waiting for a successor to Battle Isle 3 (No, Phase 4, where they turned the turn-based wargame into a pseudo-RTS does not count. Neither does Incubation, which turned it into a tactics game) and History Line...

Ironically, I had never heard of Dwarf Fortress prior to its release on Steam lol, let alone finding out how long the game has even been a thing! When I first saw gameplay, I was like "wtf is this?!?" then I started reading the insane number of positive reviews and how obsessed the community is still with the game after all these years, it really makes me want to try it. 

But, I know I'll have to spend numerous hours familiarizing myself with all the games systems. If you have any good "how to" videos on the game, please feel free to send it my way!

I know it's colony sim-lite, but have you tried out Manor Lords yet?

I started feeling nostalgic for the ost of Civilization 3 and I forgot about this smooth jazz track hundreds of hours played and will always remind of thermonuclear war

Ooooof. RIP Blue Byte. Ngl, my only familiarity with the Battle Isle series was Andosia War lol. I don't even remember how I got a copy of the game but I actually wasn't a fan of it. It was frustrating to play but I can't remember the reason why off the top of my head. 

How do the original trilogy of games hold up and is there a way to play them still?

The community is still playing it, because over the two decades the game exists the creators never stopped working on it, so it is constantly updating.

Dwarf Fortress is imposing and also not a game in the classic sense. It is a fantasy world simulator, very detailed, in which you can set up a fortress. And as the world does not care for you, some random event like a wandering monster can wreak havoc on your fortress. And the gameplay is difficult, because there are so many systems here. But with the graphic release on Steam and itch.io it is much more manageable to handle the system at least on a basic level to get your first fortress running.

Here is a starter tutorial, nothing fancy but it covers the basic needs:

https://www.youtube.com/watch?v=93pTwS6mIoc

If Dwarf Fortress is too complex for a start, maybe you want another game as entry level drug. Many of the games deriving from Dwarf Fortress ditch the 3D-world (blocky), but Odd Realm keeps that, so I would recommend it as an easier entry to this game type. This tutorial is a bit older so things might be a bit different, but I can't find a more recent tutorial:

https://www.youtube.com/watch?v=ujAmccR6z_E

And about Manor Lords: not yet, but it is on my Steam wishlist.

Graphically of course they are totally outdated, but the gameplay still holds up very well, especially on the third one, which is fully mouse-driven. 1 and History line are a bit more finicky by modern standards (best use the keyboard) and harder to plan ahead, but once you get used to the control schemes they're actually quite easy to use.

You can get the entire series (sans Andosia War, but including all the expansions as well as the spinoffs History Line and Incubation) on GOG in a nice bundle. And even more nice is that it's 75% off right now, so you can get the entire series for just $2.50 at the moment.

Edit: Here's a LP in English from Battle Isle 3 if you're interested:

https://www.youtube.com/playlist?list=PL2mVwWymK5NNlw0kUtys7ijSUgVcVMT2A

These days, I play a lot of Age of Empires 2 and Hearts of Iron IV. This summer I hope to enjoy some more Stronghold Crusader.

In the past I enjoyed such games as Civ 3, Medievil Total War, Age of Mythology, Rome Total War, Crusader Kings, Command and Conquer Red Alert Retaliation and 2.

In September, I will pick up Age of Mythology Retold and try multiplayer.

I still play: StarCraft: Brood Wars, StarCraft 2, Alpha Centauri, Master of Orion 2, Sins of a Solar Empire, Command and Conquer Red Alert 2, Dark Reign 1 and 2, Battlezone 2, Sacrifice and Dungeon Keeper, Total Annihilation, Supreme Commander, Homeworld 2 remastered and a few others.

I absolutely loved Company of Heroes, but the sequels didn't live up to that same high for me sadly.

What I really want is a remaster of Black and White... Or just a Black and White 3, but with lionhead gone and EA as one of the worst tech companies imaginable, that is a pipe dream.