Great game, good add-on
I have all of the expansions and this is about like the rest. I gave it a 4 because it is more like a 3.5, as it adds only a little. I love the Sisters and really enjoy playing them. More for the price maybe?

Nothing New
Dawn of War is a good game, but this expansion is not worth $40. Unless you love the sisters or the DE, just wait this goes in the sale bin or until DoW II comes out next yet.

Slightly rushed development - overall good game
Pros: TWO new armies. Sisters of Battle are like Space Marines, if the 'rines took all their defensive prowess and channelled it into offense instead. The "Emperor's Touch" ability is absolutely SICK - it can bring down a Daemon Prince in no time flat.

Haven't played with the Dark Eldar much, but they seem potent.

Cons: Pathfinding and combat AI seem a little buggy - sometimes a unit won't begin attacking an enemy nearby until I go through the trouble of selecting them and telling them to move (in any direction).

ALSO: THQ seems to have only half-upgraded the Necron Lord. Yeah, he can turn into the Deceiever now, but it feels half-finished - the Deceiver should have more abilities.. in its current form it's just not worth using - the Nightbringer is far more effective. Maybe if they gave the Deceiver the ability to fake-clone entire armies (to create diversions) or something similar..

Overall a good expansion but it feels like the dev studio got cut off before the normal end of the development process and put on a different project (probably Dawn of War 2) before they had a chance to really put the "THQ/Relic polish" on. Sadly this happens with a lot of great games - Xenogears, Final Fantasy 7, the list is too long to list here.

If you're a Warhammer 40K fan, and enjoyed the previous games, you'll like this one.

Lots of fun
I'm not experiencing the problems others seem to be commenting on - probably because I'm still playing in campaign mode. I'm enjoying it so far.

My biggest criticism of the game itself is that the AI on the Take and Hold missions are pretty dumb. They rush to attack your base, and usually lose, rather than rushing to take and hold the critical locations. The system map is also a little clunky in campaign mode.

Outside of the game itself, there was a marketing misstep here. I haven't found a US Games Workshop or independent store stocking Celestian squads or Exorcists, key units for the Sisters (one of the two new army types included in the game). I'd think there would be a natural tie in. Amazon doesn't have them for sale, either, even through a third party reseller.

Soulstorm, another good add-on
This add-on is very similar to Dark Crusade in that it's best played with the other games stacked on. The 2 new teams are fun and each team gets a Flyer unit (as opposed to the skimmer units). Overall, fun game with lots of killing. A good purchase for rabid fans. The game has no real downsides other than the fact that the game is starting to show it's age. The add-on doesn't change the gameplay from Dark Crusade, it just makes the game bigger: more maps, more teams, more units. No real flaws, runs great.