I liked this one better than Dark Crusade, though I don't know why.
Other than that, the game offers exactly the same campaign from Dark Crusade, only on a different setting, but that's not much of a difference. There are even fewer "story" battles this time, because there are no more special provinces except enemy strongholds. The bonuses they provide, have been diminished as well and there are no more uber powers like the Space Port or the power that allows you to attack multiple times in a turn. In fact the only two powers I found kind of useful in Soulstorm were the Forward Base and the Eldar's ability to move three times in a turn.
On the other hand, provinces are roughly the same in number which means much more skirmish battles. Since almost all of them yield honor guards, at the end of the game you will start each battle with such a huge army that you will simply attack-move it towards the other end of the map and you will be a winner in three minutes. Not exactly a challenge.
Overall, this is exactly the same game as Dark Crusade. It is better in some aspects and worse in others but still, it is the same game. On one hand, this is a very cheap way to release an expansion pack (especially a third one). On the other, if you liked Dark Crusade (there are no reasons that you didn't), you will like this one as well. It's been two years since its release and Soulstorm is a good excuse to play it again.