Total Annihilation was one of the first (if not the first) Real Time Strategy game to fully use 3D rather than a 2D based engine. It was also quite unique in it's unit/structure building compared to previous RTS games. In TA you could assign multiple builder bots to any building drastically increase the speed it was completed (depending on resources) - but you could also reclaim resources from destroyed units as well as trees and rocks. It was quite revolutionary at the time however many RTS games since have adopted these game mechanics.
However my favourite part of the game was the incidental music, written by none other than Jeremy Soule. This is one of the earlier games he worked on by he went on to write the music for games such as Dawn Of War (only the first one), Guild Wars, Knights of the Old Republic and the Eldar Scrolls series. He also wrote the score for Total Annihilation's spiritual successor: Supreme Commander.
He's often chosen because of his inventive and film like orchestral arrangements. Some have dubbed him the next John Williams, and that reputation is not unjustified! You only have to listen to one of his works to understand just how talented this guy is.
Here's a piece from Total Annihilation, which is where I first heard his stuff 12 years ago!
You can visit Jeremy's home page by clicking here! (plenty to listen to here also!)