As far as RTS titles go, the Dawn of War series is as good at eliminating a lot of the unpleasant work as anyone else, while providing a clearer focus on the action.
Few game worlds are this richly developed. Every faction has a long back story and key place in the universe. It's a more fulfilling experience wiping Chaos Space Marines out after you've read some of the Space Marines lore on wikipedia.
The sound effects and especially voice acting are excellent. Beware the alien, the mutant, the heretic.
Dawn of War was never especially attractive and nothing has been done to remedy this over the years. However, the game remains very playable and functional.
THQ should have released Soulstorm at a lower price or put more work into the expansion. As it stands, it's a borderline ripoff.