Chaos Rising is a game of choices. Will you open a defensive gate by disabling its hard-to-reach power generators, or just kick the whole thing down and hang the consequences? Will you take a lengthy detour from your next mission to save an imperilled ally planet? When an army of brother Space Marines wrongly believe you to be a traitor and turn against you, will you slay everyone you meet or sneak around them? Will you pet this cute puppy, or kick it into the nearest canal then tell the little girl who owns it that it always hated her anyway?
In theory, it's Corruption and Redemption rather than good and evil, but hell, you know the score. Each of your squads corrupts individually, bar the morally unshakeable Dreadnought Davian Thule, and as they do they gain access to even weirder, nastier powers. There are penalties to using them, but the upsides are very up - for instance, the Librarian loses his healing ability, but is eventually capable of hypnotising enemy units to fight for you, or summoning a small horde of big, red naked demons.
Thing is, you're not simply deciding to be Shiny Pure Guy or Dark Malicious Nutter. You're juggling a whole bunch of micro-factors in your mind. You might want Jonah's sinister Subjugate power, but you also want Avitus to remain Pure so that he can wear an especially powerful suit of Terminator armour that requires him to have an untarnished soul.
Optional quests and deliberately lame items can remove corruption - but ignoring or rushing side-missions and donning especially tasty wargear will push it up. This system is simultaneously joyous (especially due to the increasingly confused squad leaders' bickering about your/their actions) and a little annoying.
There are a few too many Corruption-gaining conditions, such as not taking certain characters on a mission, deciding not to take an otherwise-optional diversion and activating special powers that twist the soul of everyone you've got in play. Sometimes, it's a bit like being bullied - do this chore, or I'm telling your dad!
Then again, it's a pretty good reflection of the stony-faced, sleepless dedication to the Emperor that all Space Marines are required to demonstrate. It's just a bit of a shame that it's so numerical - you're told Tarkus will be corrupted by a specific number of points if you take him on this mission. Really? He knows exactly how evil he'll become just by looking at the planetary shuttle and thinking about what he's in for?
While DOWII has always been a statistical balancing act, it's a shame the slide towards Chaos isn't more organic. I'm pretty sure Nurgle isn't worried about numbers as he's busy subsuming entire galaxies in pestilence.
Still, it's a great way of making you care about your troops, and adds a welcome layer of thoughtful management to the frantic loot-collection. Decisions on and off the field now carry import; it's rarely a matter of killing everything on the map and then equipping the highest-level stuff in your inventory.
The mission structure has been overhauled to be less shallow, too. Chaos Rising is mercifully free from the infuriating repetition of its predecessor, each main mission a happy bundle of scripting, spectacular environmental destruction and brief mid-scrap cut-scenes.