You should try Dawn of War then. It's based off of Warhammer 40,000, but it's RTS. So, it's all the fun of the game, but you don't have to paint or build miniatures. And the games last about 1/3 as long.
http://www.dawnofwargame.com/
And yes, Total Annihilation is by far, one of the best games ever. The sheer size of it is awesome. Some of those maps take foreverrrr to play.
Biggest Map on there is, I forget the name, but it's the water level on Core Prime. It's huge... I think it's called 7 Islands.
Naval battles get crazy, then bringing in amphibius units up their ramps into their base. Or unloading units off of the transport ships... beach landings!! Rahhrrh!
Best part about that game, is that you could load up a builder unit with an infinite amount of work, just holding the shift button and he'll build something and go onto to build the next unit in the que. OMG that's such a sweet feature.
Or putting builder aircraft on patrol over your base, and letting them repair anything within their path whether it's defenses or units. Golden!
Must go find my TA cd's now.