Gameplay
Definitely the biggest section, but it can be summed up as: more of the same. Which is fine for Dawn of War-it continues to be an aggressive game, especially now that teching has been nerfed across the board. The AI in Soulstorm is much more aggressive than it has ever been, and now can give you a decent run for your money as you prepare for online play-even in the campaign, a strength 3 territory is liable to be throwing vehicles at you if you dawdle. Otherwise, the changes come from the two new races and the new units, as described below.
Two more races from the rich WH40k universe make their debut in the Dawn of War series: the witch-hunting Sisters of Battle and the depraved Dark Eldar. Both fit in just fine with the existing races, and aside from a nasty bug each in multiplayer, are neither overpowered nor underpowered out of the box-quite a relief to Dark Crusade veterans! Both also use a new resource-souls for the Dark Eldar and faith for the Sisters, which manage to fit just fine into existing gameplay. Unlike the Necrons, the DE and SoB economies require active and aggressive play.
As for the Dark Eldar themselves, these are the darker and more twisted cousins of the familiar genocidal space elves Dawn of War fans have known from the get-go. They play like the Eldar taken to their logical extreme-fast, hard-hitting, and very fragile. The Dark Eldar are perhaps the fastest race in the game, being able to bring out vehicles as early as t1.5, gaining no fewer than two jump infantry units and even a jump-capable vehicle! They are also very, very good at breaking the morale of their enemies-they have a number of special abilities that damage morale, and they are quite adept at ruthlessly breaking even the staunchest foes. Some of their other dastardly tricks include their anti-tank infantry unit having jump packs, a special ability for their commander making your own squads attack each other, and an ability that makes your infantry run away in fear. Dark Eldar soul powers are worth noting-these are what you gather souls for, and they vary in strength, from very useful to very meh-the eponymous Soulstorm power in particular is a disappointment. Micro-fiends will find lots to love here, and the Dark Eldar ooze evil. Oh, and watch out for their relic unit-the Dais of Destruction is very fast for a relic unit, and has a nasty ability that cuts down just about everything in front of it-and it can be instantly recharged with the proper soul power. Plus, it has a couple of rather scantily clad slave girls on its deck for bonus points.

The Sisters of Battle, on the other hand, are the militant wing of the Ecclesiarchy-working with them is limited to pointing at the enemy, shouting "HERETIC!!!" and praying they don't come back for you. Gameplay-wise, they can be thought of as the middle ground between Space Marines, Imperial Guard, and Eldar. They come in larger numbers than Marines, are tougher than Guard, have weaker vehicles than either, have lots of special abilities, and can bring more anti-tank weapons than you can shake a stick at. With proper micromanagement, the Sisters are truly fearsome-the missionary and confessor are key here. In addition, the Sisters can be perhaps the best tank-busters in the game. If they decide a single enemy vehicle (hello, there, mister relic vehicle) absolutely must die, there ain't much you can do to stop them. Finally, the Sisters have some serious style on their side. Strapping a sinner onto the front of a giant walker with claws and shoulder-mounted flamethrowers and sent forth to die? Check. Barely-dressed assassin dual-wielding swords and using lots of acrobatic moves? Check. A vehicle whose weapon system consists of a big church organ mounted on top with a guy in front of the organ (still sitting on top of the vehicle) playing the organ, complete with sheet music stand? Check-oh, and the organ is actually a multi-rocket launcher. Scantily clad ladies with two-handed chainswords bigger than they are? Check. Sounds like we got a winner, folks.
Another thing Soulstorm makes a big deal over is air units making their debut-I think my box said "Air units redefine the way war is fought!". Nothing could be further from the truth-air units do in fact fit in just fine, because they're basically just vehicles that ignore terrain and can't be attacked in melee, so treat them like any other vehicle, only with buggy pathing. Of the air units, only the Tau Barracuda stands out as a truly useful air unit, though the SM Tempest, Chaos Hell Talon and the Eldar Nightwing aren't bad. Not great, but not bad. Of the remaining air units, they range from very niche-y (SoB Lightning, DE Raven) to waste of resources and vehicle cap (Ork Fighta-Bomma, IG Marauder, Necron Attack Scarab). It really does feel like Relic is testing how to use air units in future Dawn of War games-as it is, it seems rather half-baked.
And that brings me to the single-player campaign. First of all, you've got all three Imperial factions at each others' throats for rather flimsy reasons. But this is a game showcasing a free-for-all between the nine races, so I'll let that slide. What I won't let slide is the utterly sloppy nature of the campaign-that each commander at the race selection screen uses the same pose and animation as in Dark Crusade is a warning. The lack of a race intro video for each race is another. The campaign itself is shoddily done-you don't keep buildings you build on each map anymore, but the AI still gets its enormous honor guards, and a s10 province can have you facing predators less than thirty seconds after game start (I'm speaking from personal experience here...). About half of the Chaos honor guard still refers to the new Chaos Lord as Eliphas-even Carron's daemonic ascension calls him Eliphas. Stronghold intro movies and victory narrations are likewise mediocre (warning: the Chaos stronghold intro video wins the award for worst voice acting in the entire game). However, the core gameplay is still solid-the strongholds are much tougher this time around, Orks and Marines aside. There will almost always be pressure on you to stay active and moving-you can't comfortably turtle and tech up like in Dark Crusade during most strongholds.
Oh, and there's no more commander trash talk. Boo.
So in summary: the core gameplay is still good, but the air units and campaign are both very sloppy. Luckily, it's the former I'm most concerned about, but just the sloppiness and the lack of commander trash talk in the campaign hurts.
Rating: 7/10
Graphics
The DoW engine is definitely aging, but it still runs fine on older computers, and the Sisters, DE, and new units alike are all detailed and good-looking. However, many older units suffer from missing textures, and the new races have a paucity of sync kills. But as a whole, it still looks good. Not great, but good.
Rating: 7.5/10
Sound
As is the trend, the sound is mostly good, but with some glaring disappointments. The new units are all well-voiced (the missionary may get on some folks' nerves, but I like him, and the scourge and dais of destruction have great voicing), and the new commanders are as well, utter imbecility of the new Chaos Lord's lines aside. Some truly inane and stupid dialogue, but well voiced for the most part. Unfortunatley, the narrator has gotten worse since Dark Crusade, and some stronghold intros feature truly bad voice acting by lesser characters.
Rating: 7.5/10
Overall Rating: 7.3
Soulstorm is a technically good expansion-the core gameplay has been improved and nothing new is out of place. But it sorely lacks polish, and definitely has the hallmarks of a rushed job. In the end, I'd recommend waiting until the price comes down-40$ just isn't worth it.