Heh, I believe I played Achron (chess like) on a C64, don't recall the time travel aspect. I never played Dawn of War 1. In any case I enjoy being able to control time from 1.5x faster than normal, all the way down to literally zero (paused) if you want.
One annoying thing (even if it's an intentional part of the game), when a unit dies, it doesn't tell you which unit. Most importantly if you are trying to level up your units, it doesn't tell you if it was a unit that gains experience (like all fighting units), or doesn't like a truck or repair unit.
Took me 5 minutes to track down the line of code and add a print statement.
And even less unique in low budget / open source RTSes ?
Special mention to Achron with literal time travel as a game mechanic !