I picked this up about a week or so ago and installed it, but hadn't given it a shot yet. Man, I'm so glad I did. This completely, completely renewed my love for all things Dawn of War.
Firstly, the campaign is just awesome. It's bigger, better, there's more to it, and it builds on everything that made Dark Crusade fun and different. I'm not sure about the difficulty idea yet since I haven't gotten too far in, but I expect this is a bit like Dark Crusade in that things get a bit easier as you progress (at least as far as the normal battles go) because your hero gets so much more powerful and your retinue expands. Anyway, you've basically got the same elements as far as I can tell, there's just more to it and a little more strategy that can be used.
I haven't tried the Dark Eldar yet, and more than likely won't get into them much, but holy crap I love the Battle Sisters. For those who don't know, that's who I decided I want to paint for the actual tabletop game, and though it's been obscenely slow going for me due to an overabundance of other hobbies and real-life issues, I still really love them. I can say pretty much without reservation that they're my favorite faction, even though I like a lot of the others a lot too. But it's really nice to see that I love them just as much in Soulstorm as I do with the minis. They're just so fucking fun to use! It reinforces my confidence that going with them for tabletop was really the right decision. I love all the units, and I feel pretty confident with them if I make the right choices. You can make some incredibly killer infantry if you use correct upgrade paths, and their vehicles are very fun. Add in the Golden Saint uber unit, and I'm happy as a clam. These girls just feel like home, and I'm totally into finishing the campaign with them.
So just what I needed, another game to play! But I'll be damned if this hasn't rekindled my love for DoW. If you ever liked the game in any capacity, give this a try. The sandboxy campaign seems just as fun as Dark Crusade's was, and I'm quite sure multiplayer matches will happen again with those of us who grab it at some point. I'm far from a good competitive player, but I'll still play some matches, and anybody who enjoys coop is certainly welcome to hit me up for a coop versus CPU game too.
EDIT - And you know, the game still doesn't look bad. It's showing its age now in terms of individual units being quite blocky and such, but at the level of view you generally play at (and even when you're zooming in a bit just to watch things die) it really doesn't matter. The game still looks great, and the audio is there too with great music and at least most of the unit sounds being fun and cheesy in the *good* way. I don't feel like this game has aged badly at all. It isn't the best looking RTS on the market by any means, but when you crank everything up it's still very far from unattractive, and watching huge battles is still exhilarating.