TA takes a little to learn the true beaty of the game. At the simplest appeal is the obvious - I hit unit limit of 256 in TA without breaking a sweat. I can handle armies of over 500 with trouble. StarCraft makes commanding more then 10 units at once a pain.
TA, SC, and Dark Reign are the 3 major approaches to RTS design. SC has small unit counts, each unit is complicated and detailed, and has specific interactions with each other unit in the game. This limits the game to small unit counts - you command small squads specifically, using their powers specially.
Dark Reign goes for squadren based approaches - you do formations and teams of units, but large teams. It feels complicated and kludgy.
TA throws the details out the window. Your army has become a massive, living, breathing organism. The little units are nothing more than cells of the beast. You learn to think in particle systems - clusters and patrol zones. The units are simple - they each do a job. You throw them around - you learn not to command individuals so much as conduct the orchestra. And yet, it does this not with Molyneux-esque ambiguity, but with direct commands - you control the units directly, individually, but you don't think of them as individuals.
TA ends up feeling not like a simulation or a game - not like you were trying to approximate a real-world or hypothetical environment (as games like DR feel) or like you're in some rule-encrusted hyper-chess like StarCraft - it feels like its there. It feels like there is a little world of Morty's, Commanders, and Construction aircraft running around, and your little mouse is trying to control it.
TA is cool.
Z and Battlezone are good too.
