Like Warcraft III, character units play a large part in the ebb and flow of battle. Commanders tend to be deadly in melee, and they're tough as old moon boots, so deploying them at the right time can make all the difference. Many leaders boast special abilities, such as the psychic Eldar Farseer, who can be upgraded with a number of devastating psionic powers designed to damage and disrupt enemy forces.

There are two other key factors to exploit in combat: morale and cover. Different units have different levels of morale, and if they lose enough of their number, they'll break. Breaking doesn't mean running away though - it's up to you whether you retreat a broken unit, and they'll actually get a speed boost if you do, to represent their bottling it. Keep them in the fray however, and they'll fight at seriously reduced capacity, reflecting their broken spirits. Certain weapons, such as sniper rifles and flamethrowers, break morale swiftly, which can prove invaluable in front-line assaults. Cover, which comes in light and heavy flavours, does exactly what it is supposed to, providing your troops with defensive bonuses when they're in it. Very handy for by-sections advances, and defending key areas.

The game is divided into three modes of play: the singleplayer campaign, skirmish vs CPU games, and online multiplay. Those hoping for a campaign for each of the four races involved (Space Marines, Chaos, Eldar and Orks) will be disappointed, for there's only the one, playing as the Blood Ravens chapter of the Space Marines. During the campaign, you'll contact the other three races and you'll also briefly control a few units of Imperial Guardsmen - the human militia of the Warhammer 40,000 universe. The missions are enjoyable and well-paced, throwing increasingly heavy challenges at you, then slackening off to give you a chance to play with the new toys in the Marine tech-tree, before launching into the later, more complex operations. Throughout its course, the campaign introduces you to every unit in the game, and very much reflects the tenets of the 40K universe, dealing as it does with racial manipulation, daemonic possession, betrayal and ceaseless conflict. It's also a good introduction to what is really the heart of the Dawn of War experience: multiplayer matches. By then you're thoroughly schooled in base building, resource acquisition and combat with a wide variety of units. Naturally, the latter applies only to the Space Marine forces; learning to use the other races is up to you, and player-vs-CPU skirmishes are naturally the best place to broaden your horizons.

Just like in the table-top game, most players will get to grips with the Marines first. You play them, in the campaign, but they're also the most accessible race, and therefore the most forgiving to the beginner. They field tough troops and vehicles, and are good, safe all-rounders. Chaos, the eternal enemies of the Marines (and pretty much everyone else), field some similar units to the Marines, but there's a distinctly daemonic bent to their forces. Their nastier troops get a wide variety of savage melee upgrades, and daemons get a look-in, most notably the immense, horned, axe-wielding Bloodthirster.

The Orks are different again. Their strength lies in their numbers, and as you mass their ranks, their more advanced units become available. This reliance on population to dominate is reflected by the army's Waaagh! Rating, and the higher this is, the higher the Orks' morale is. Get enough Orks on the battlefield, and their spirit is virtually unbreakable.

Which leaves us with the Eldar. They're probably the trickiest race to play, owing to the fact that their tech-tree can be pushed in many different directions, but they're potentially the most rewarding as they field advanced weaponry and a devastating array of psychic powers. Brittle and fast-moving, their attacks must be co-ordinated swiftly and efficiently. However, if used well, they're capable of reducing an enemy's forces in a very short space of time.

And once you've got the hang of an army, it's off to the multiplayer servers you go. Online play is the greatest test of your abilities, and the four finely-balanced and versatile armies can make for some titanic, sweaty struggles. There are many optional victory conditions, our favourite being timed territorial advantage games, in which you (or your team) must hold more strategic points than your opponent(s) for the course of the game. You'll see bitter fighting over certain strategic points, and success demands that you're fluid with your approach - both reacting to the enemy's posture and snatching strategic points where you can while his attention is elsewhere.

If you know your 40K, you'll get a head start in Dawn of War, as you'll know that a lascannon is the perfect anti-vehicle weapon, for example. And for those in this category, you'll love the faithful and vivid reproduction of 40K units, and the way they're brought kicking and screaming to life. For those who aren't interested in tin soldiers - you'd be nuts to miss the finest sci-fi RTS to hit the PC since Total Annihilation.

Warhammer 40k: Dawn of War is out now on PC