Dreadnought Davian Thule - still one of the coolest units in RTS gaming - is holding the line at the bottom of the map, but he can't hold it forever. You rush to save him, with the powerful librarian Jonah Orion - the Space Marine's new elite unit - in tow. In Dawn of War II, you might have moved down the map in a breezy fashion, saved Thule, and instantly forgot the act. But in Chaos Rising, all sorts of hell breaks loose as you frantically scramble to Thule's position. Ice cliffs crumble and fall as you pass through valleys. Glaciers shatter and slide down into the water below, preventing any retreat. It feels as if the world is falling apart right behind you.
Another example: one of the game's best missions sees the Blood Ravens explore the dark and dank corridors of a Space Hulk (remember that board game?). There's little room to manoeuvre, and it's quiet - too quiet. Then, of course, the terrifying Tyranids, bolstered by Genestealers (yay!), literally burst out of the walls and head straight for your armoured flesh in a flurry of claws and razor-sharp teeth. Carnifexes blow out of pipes, leaving twisted metal and steam in their wake. You can see little monstrosities crawling about all over the place before they even get to you. It's brilliant - atmospheric, scary, and totally, totally, Warhammer 40k.
Then there's Corruption - a neat new feature that adds a degree of morality to the bloodshed. At its most basic, each of your units can be corrupted by player decisions: do I battle back a Chaos uprising by destroying the great gate that defends Angel Forge, or use Jump Packs to take the long way round? Do I take care not to destroy a Blood Raven monument as I assault a group of Chaos, or rain down orbital bombardment and missile launcher fire from a safe distance with nary a care for relics? Do I care about entirely optional, pain in the arse redeeming missions, or get on with the good stuff post haste?
The game always makes clear which decision will result in corruption, so don't expect any philosophical head-scratchers, but it's cool all the same. More interesting is the use of special corrupted wargear and the pursuit of cool traits unlocked by climbing up individual unit corruption skill trees. If some wargear is used in missions, it'll add a couple of points of corruption to the user. Now, the question you have to ask yourself is, do I want corruption? Some of the corruption abilities look the business and are incredibly useful on the battlefield. But climbing up the corruption ladder prevents you from using other wargear designed for the pure of heart and mind, and takes away already unlocked traits. So, as you're fussing over equipping Terminator armour to your Force Commander, and working out which heavy weapon to give to Avitus, you've always got corruption clawing at the back of your mind. You think, I really want Jonas to walk around the battlefield covered in flames, but if I head for that trait, I'll lose his incredibly useful healing trait. Really, that's what the corruption mechanic boils down to: loot and traits. This isn't a criticism - you genuinely care about your men and their tools of destruction, itself an impressive achievement. Just don't go expecting a Fallout 3-style karma system.
All the while, though, you wonder, is this going to impact on the storyline in any way? Are my decisions going to meaningfully change the tale Chaos Rising is telling? I won't spoil it for you - even though I really, really want to - but I will say that the answer is yes. Corruption adds replayablity to the game beyond just maxing out the level 30 cap and getting the best wargear. Chaos Rising has multiple endings, and with good reason. I'll let you discover them for yourself.