Al (most?) of the other RTS games are very resource constrained. So, you have to focus on tight unit mixes, concentrate on individual battles, doing micro, and running about.
TA is more a game of raw tonnage, not of finesse and subtlety.
As the same time, original TA is notorious for not being finely tuned or balanced. And I'm sure that's much more important in PvP.
But in PvE flinging two industrial powerhouses against each other, where subtlety is replaced by 100, throwaway, Flash tanks, it's just a different play experience.
Bullet hell, or rather bullet heaven. TA was the first game where I saw the PC struggle during big battles and it was a pleasant experience, unlike the lag in multiplayer games where I mainly played against people across the pond.