If you're all about the amorphous role that is 'support' you'll want the trickery of the Chaos Sorcerer, who gets a few summons of his own, can teleport a bunch of lads all over the place, and can turn invisible. In other words, despite some of the more superficial similarities to the existing Space Marine faction, Chaos are a much more devious bunch than their pure-military nemeses. They look and feel good on the field, falling somewhere between the Marines' stout gunplay and the Eldar's otherworldly weirdness.
DOW2's unit count always felt a bit meagre compared to the gigantic army roster it ended up with after three expansions, but introducing a fifth faction, and especially one of the most iconic ones in the 40K universe, palpably livens things up - making for a much fuller-feeling game. In other words: barring an enormous balls-up, Chaos Rising is likely to be about as must-own an expansion as DOW2 could possibly get.
The aforementioned Chaos Sorcerer, incidentally, carries over to the expanded Last Stand mode. In case you've left DOW2 gathering dust since launch, it's worth explaining what that is. A recent patch introduced a new multiplayer mode, intended as a response to solo campaign-orientated players who felt that the main multiplayer mode was too dramatically different, and brutally inaccessible, to the single-player game.
Last Stand's entirely co-operative - it's you and a few chums (or random pick-ups) controlling just a single hero character, and fending off as many waves of AI enemies as you can before turning into so many sticky red puddles with bits of spiky armour in. As you do so, you level up and unlock exciting new pieces of wargear.
It's simple but super-fun, and with none of the daunting skill requirements and cries of noob suffered by those who don't know the chapter and verse of online RTS brawls. Though it's worth mentioning there's a new two versus two traditional multiplayer mode for those who are pre-converted.
In DOW2 core you can only play Last Stand as Space Marines, Eldar or Orks. But if you own Chaos Rising, the titular Chaos and the Tyranids (specifically, their Hive Tyrant) enter the playable fray. Oh yeah - which races you have access to depends on which versions of DOW2 you own. If you own both DOW2 and Chaos Rising, you get the lot, but if it's just Chaos Rising you only get Chaos and the Nids.
Also, only having CR installed gives you the new single-player campaign and the option to play as either Chaos or Space Marines in traditional multiplayer, but none of the other races. Relic doesn't want to split the fanbase, however, so there'll be a day-one patch for DOW2-core that enables folk who own just that to play against people who own both games, or just CR. Which means Chaos and the assorted new units for the other races will be folded seamlessly into DOW2-core, for free - they just won't be playable.
CR's new multiplayer maps will be, though. So, while CR may suffer the now-traditional expandalone curse of carrying an oofsome £25 RRP, at least no-one's being left out in the cold, staring mournfully at empty multiplayer lobbies because they can't afford or don't want to shell out for CR. There'll also be a Gold edition, containing both DOW2 chunks, released at the same time, for around a tenner more than DOW2-solo.
This is all on top of an expanded, rebooted single-player mode that ditches the tiresome glorified skirmishes in favour of set piece-laden, bespoke missions throughout. If Chaos Rising can get all its mutant ducks in a row, it could be as much a do-over for a somewhat troubled game as it is an expansion for it. Even the gripiest of Dawn of War II gripers must admit there was something good there, underneath some wobbly implementation. Chaos Rising should make it all okay. Even if it doesn't, hey - Genestealers!
Warhammer 40,000: Dawn of War II - Chaos Rising is due out for PC on 12th March.