Urtuk: The Desolation

Urtuk: The Desolation is a turn-based tactics game, where you control a party of (up to) 6 characters in a series combats on hex grids.
The strength of Urtuk lies in the depth of the combat system, and in the amount of content built around that combat system. There's about a dozen classes, probably over a hundred different traits (passive abilities), a bunch of different equipment with various modifiers, and a progression system for characters that allows them to not just gain levels and stats, but also unlock new traits by completing certain actions in combat. There are also mutators, which are equippable traits that can be harvested from enemies you beat, and can eventually be absorbed, becoming a part of the character equipping them. Characters falling in battle results in an injury that's difficult to get rid of, and further leads to the character permanently dying. (But you can find a new one.) While there's a random element, it really feels like the way you play shapes your characters' progression.
The combat itself makes excellent use of terrain elevation, obstacles, and a lot of interaction between different units. Taunting, retaliation, support attacks, pushing, evasion, and a lot more. Most movements and actions are very important, as it's difficult to get out of a tough spot once you're in one, so some planning has to go into making sure you don't spiral into losing teammates, thus making further encounters even more difficult.

I would say that Urtuk has the best turn-based tactics combat system out of all the games I can remember. But there is a problem. The combat system is the entire game. The overworld has basically nothing. You can move from place to place, various events spawn, but they're all some form of combat encounter. There's some variety, where not everything is an all-out deathmatch, but that doesn't really change the essence of the combat.
It was really interesting playing these combat encounters back to back for the first couple of hours, but I eventually felt myself feeling a lack of purpose. Yeah, I had some vague quest and storyline to follow, but I didn't really feel like I was making progress aside from just completing yet another battle. There was basically no incentive to pick and choose my battles, and each combat either boiled down to a victory from which my units escaped unscathed and stronger than before, or a debilitating defeat. Mostly the former though, as the AI was a bit lacking in how it approached the battles. After a while, I also discovered some stronger strategies, like putting two tanks in a chokepoint and using four ranged units to obliterate anything that came near. Or abusing the action economy and putting all points into the stat that gives speed and stamina, making up to 6 times as many attacks each turn as the enemies. They did have harder difficulty modes, so perhaps that's not a problem.

Regardless, I can only give this a partial recommendation. If you want to just grind out tactical battle after tactical battle, then maybe there's something here for you. Sadly, probably due to this being made by a very small team, possibly even just a single person, there isn't anything else to do. I loved the combat, but it wasn't exciting enough, or I didn't feel enough progression, or enough reason to go through yet another encounter. Whatever the reason, I become bored as I slowly settled into some strategies that worked out for me, and I never reached the excitement to play just one more battle.