Dota 2.
I've played Dwarf Fortress, Stellaris, yet I still find Dota to be the most complex game ever.
It sucks that it's a multiplayer game, and you need people to play it well with you, but when it works, it's amazing.
Everything in it has layers of usability, usually componded by the everything else in the game - hero abilities, items, map, neutrals, even the stupid trees play a large role in the game.
I've spent hundreds of hours studying the mechanics, and I still don't grasp everything.
I played a lot of DotA too, but that doesn't have a playtime counter. But I have over 3000 hours in Dota 2.
My second favourite game is OpenTTD. It's just so satisfying to optimize the train network and add another 100 trains to it. I've tried Factorio, but for some reason that did not scratch that itch.
Or some roguelites, like Slay the Spire (or the Touhou: Lost Branch of Legend), Synthetik (haven't tried second one yet), they are always fun.
LoL sucks, it's like a shallow copy of DotA. I've played around 300 hours, it's very silly in comparison.
Stellaris is kinda easy once you figure out that expanding is the No1 priority for the entire game. Expand, build ships - nobody will be able to stop you.
There was always a need for a 'tall' empire - so you don't expand, but focus on your small part of the galaxy - but so far it's always crushed by the expanding ones.
Once you get stargate tech, it's 24/7 war. For even more territory.
Right now I remembered a game that never was really finished, Stardrive, where you could design your own ships down to the electrical wiring. It had layouts with sections, and you could fill it up to your liking. It was a shame that ground troops could finish the game in minutes.
Sometimes I feel like 4X games are usually more suited for roleplaying than actual challenge of micromanagement.
Anyway, I have a huge jam on my main line in OpenTTD, gotta fix my intersection again.