I've been playing lots of old games recently.
If you want Epic, just get Homeworld. Possibly the best single-player story arc I've yet seen in an RTS. No other game captures the vastness of space or hits with the same emotional impact as Homeworld 1. And the graphic design is un-frickin-believable.
If you're thinking indie, check out Tread Marks.
http://www.ldagames.com/treadmarks/'Tis the best tank racing game ever. Which, admittedly, isn't a very crowded genre. Nonetheless, the sight of a T72 catching big air, or a cruise missile descending from the heavens to blow the living fuck out of some poor sap, is a truly beauteous sight.
Elsewise
Freedom Fighters
An older XBox/PS2/PC game, and really cheap these days. The premise: The Soviets have taken over the US, and as a NYC plumber, you must rally the resistance and make New York safe for mom's apple pie, democracy, and other such shit. This delightfully retro premise is backed up with slick comic-style graphics, seamlessly integrated squad AI, and no lack of ways to misbehave with a molotov cocktail. Fragging commies never gets old.
Ground Control
A nifty 3D RTS that actually takes advantage of teh 3D aspect instead of being Starcraft with polys. Instead of base building and resource management, Ground Control is almost chesslike in that it revolves around the intelligent usage of a smaller number of battlefield assets. The graphic design is impressive; while the game is definitely low on the polys, touches such as tread marks in the sand, sprays of shell casings, and jet contrails as Aerodynes make their strafing runs are used liberally, making it an arresting experience. GC could be described as somewhere between Close Combat, Homeworld, and Total Annihilation.
