The first Age of Empires!
Hahaha nah in all seriousness,
Company of Heroes is probably in terms of quality the best RTS ive played, but I have more fun with Dawn of War Dark Crusade.
Dawn of War DC is a more 'traditional' type of RTS base building and stuff, but instead of hiding away hoarding resources you have to go onto the map and capture areas for points used to call in units and buy stuff.
Its a real fun game that begins with small skirmishes with scout units and then turns into massive battles with lotsa tanks and big explosions.
Its also incredibly balanced for a game that has 7 races each with over a dozen units.
You dont have to be a genius to play it, it doesnt require much thought or strategy once you get the bigger units, but it doesnt matter because the battles are so damn fun to watch, big walker robots slicing people up, flamethrowering them then chucking their lifeless bodies at their buddies, 20 dudes with machine guns laying into a big monster as it stomps around breaking stuff, low level infantry being swarmed by monkey dog things.
I found campaign a bit boring second time around though, but first playthrough i was like woah.
Then theres mods.
Of course it is based on the tabletop game Warhammer 40'000 but i havent played it and im not really steamrolled by the games universe and story.
Company of Heroes is more about organising your units and keeping your squads alive, you have to use cover and cant just rush a machine gun without having at the most one and a half men left.
As in DoW you have to go out and take and hold positions for resources.
Although you will build a base, later on the more powerful units are usually called in from off map.
Unlike other RTS games you can chose one of three doctrines for each side which will grant you special powers like air support or the ability to call in a freakishly huge tank to crush everything.
Depending on your army (theres the US Army and German Wehrmacht in the original CoH, the expansions add the Brits and German Panzer Elite) these doctrines will do something along the lines improving or calling in better tanks, another will be geared more towards infantry, and the other will be more focused on support and defense.
The only problems i have with it are that Allies must always fight Axis, you cant have any kind of free for all, and i find the game unbalanced in some areas but nothing major.
As a wise man above me said 'think 'Relic,'' but if you want a decent game dont even consider Halo Wars, Ensemble has totally run outta steam.