You may have heard of Warhammer 40,000: Dawn of War, which blasted away the competition back in 2004 to take Game of the Year honors in Computer Gaming World. Relic has been making RTS games long enough to know not to fix what ain't broke -- which is why Winter Assault improves by degrees rather than reinventing the proverbial wheel.
RULE #1: Never bring a snowball to a blaster fight.
One glaring flaw in Dawn of War (depending on your play style) was the unforgiving "the best defense is a good offense" multiplayer, in which victory inevitably went to whoever could produce the largest number of cheap units the fastest.
Winter Assault levels the playing field with the addition of a new faction: the defensively-minded Imperial Guard. They may be less exciting to look at than the four other races, but the role they play in balancing the game makes up for it. With the Guard on the roster, heedlessly rushing into combat at earliest opportunity is now a risky proposition at best. While their cousin Space Marines are trained killing machines who live only for combat, the average Guardsmen probably has a wife and kid they write home to -- which means they won't part with their lives unless they absolutely have to. Couple this with the fact that they're no match one-on-one with any of the other races (even the puny Eldar), and you can see why they prefer to shoot from behind the relatively safe confines of a bunker or ATV. Not surprisingly, this means your squads can be relied on to turn tail and run at the first sign of trouble.
If you absolutely can't allow your troops to head for the hills, the Commissar unit has the ability to execute a friendly soldier in order to scare the rest into staying put. Or you could go up the tech tree and produce some Ogryn, who are too stupid to do anything but what you order them to.
Single player boasts some marginal improvements, but still remains less satisfying than the thrill of combating a human foe. To summarize the plot: a Titan (a weapon of unspeakable power crafted by the Imperium) has crash landed on resident ice planet Lorn V, so the race is on between the various Warhammer 40,000 factions to take control of it before anyone else can. With a mediocre story poorly told through weak voice acting, chances are you're not going to care about much more than grinding your AI opponent into the dust.
There are ten missions total, divided up evenly into an Order (Imperial Guard, Eldar) and a Chaos (Orks, Chaos) campaign. On the fifth and final mission you're forced to choose a faction, so I suppose the grand total can be boosted up to twelve if you're motivated enough to play through the last mission again. Also, each race has received a new unit to to make up for their inherent weaknesses: Chaplains can be attached to a squad of Space Marines for a boost in ranged attack power, Chaos Space Marines can augment their close combat abilities by upgrading into Khorne Berserkers, Eldar Fire Dragons quickly take down vehicles and buildings, and Ork Mega Armored Nobz can soak up a great deal of punishment so the rest of the horde doesn't have to.
While Winter Assault doesn't mess too much with formula or add a flashy new alien race, it makes an already great game even better. If you ask me, that's all you can really hope to get out of an expansion pack.
(****4 out of *****5) Warhammer 40,000: Dawn of War -- Winter Assault is rated M (Mature 17+) by the ESRB for Blood and Violence.