Age of Glorantha total conversion for AoW2:SM. Squads instead of the individual units of base game + more interesting use of unit abilities and resistances.
Clash - old potato turn-based strategy with tactical combat, unit morale affecting their performance, some town logistics (transporting resources between towns in convoys, diseases from overpopulation), Christians vs Pagans and marrying ugly German gold digger princesses. Supposedly there was an English version of it.
Cultures series - Settlers-like with vikings that will starve if you don't keep them fed.
Dark Reign - fast-paced RTS with obstacles and terrain affecting line of sight.
Deadlock 1/2 - suffers from snowballing effect where if you get ahead of the tech race you're bound to win, but it's still fun nonetheless. Has base building on grid map in each sector. The sequel comes with some additions but has low, blurry full screen resolution (vs crispy maximized window of the first game).
Dominions 4/5 - if you're into autistic micromanaging thousands of units and watching the AI trying to execute your orders given before battles.
Etherlords - King's Bounty with Magic: the Gathering combat.
Gruntz is more of a real-time puzzle game, but it had a skirmish mode if I recall correctly.
Jurassic War - you'll have nightmares involving its lack of pathfinding but other than that it's a nice RTS. Units have several stats and you can select which ones will increase after they get experience from killing things. There are multiple tribes to choose from, each having access to different gimmicks (crafting specific items, having access to powerful magic or dinosaurs), though later on in the campaigns you conquer other tribes and are able to use their buildings and units.
Majesty - has your usual town/base building but you can't control your units outside of offering them "quests". Don't touch the "sequel"/remake.
Metal Fatigue - RTS with three map layers (platforms in the sky, surface, drillable underground tunnels) and some customizable mecha units (you can also replace limbs/weapons at any time by stealing them from defeated enemies or using those to unlock mecha techs of other factions)
Re: Original War, depending on whether you find being able to break scripting/AI in your strategy games "immershun breaking", I think there was a mod fixing abusable scripting parts in the campaigns (but at the same time upping the difficulty a lot and it's not like you know what you can break). Also - despite game's claim, the Russian campaign is actually easier as Russians have better weapons and better breather missions, whereas Americans tend to be pitted against technologically superior opponents; there are some references to the American campaign in it that you may miss though.
Persian Wars (same engine as Black Moon Chronicles) - a mix of CYOA (on world map level), puzzle-like real-time combat (for most encounter maps there's usually an optimal way of doing things and various scripted events that may drastically affect your chances of winning, or change win conditions) and a bit of resource management (you may end up in an unwinnable situation because you kept losing troops over multiple missions and made poor CYOA choices).
Power Dolls - turn-based mecha tactics with some loadout customization.
Praetorians - don't remember much about this one outside of having fun with it and it probably focusing on unit management/combat instead of base-building.
Robo Rumble - RTS about designing mecha and pitting them against enemy mecha.
Submarine Titans - underwater RTS with lots of depth.
The Great Battles of Alexander/Hannibal/Caesar if you don't mind wargames.
Theocracy - real-time with pause strategy but time (as in, days/months/years) only flows in world map view, with building available in each province and buildings taking time to finish. Resources need to be transported between provinces, too. If I recall correctly, it had several campaigns with quite different goals but the main one is about creating an empire and then repelling Spanish invasion.
Tzar - cool RTS with a few RPG elements
War Diary - a forgotten Korean Warcraft clone.