I recently bought a new PC strong enough to run DoW 2 at full spec - this game delivers on all levels. The campaign has been redesigned and has become more focused on the player; you create a fledgeling Space Marine Force Commander, newly promoted and tasked with defending the Emperor's people from the marauding aliens of the 41st Millenium.
You are in command of your Force Commander (you) and 3 unique Space Marine squads at any one time, each with their own strengths, weaknesses and abilities. The Devastator squad, for example, are heavy weapons specialists and can be equipped with anit-armour equipment to make short work of any large targets, while the Assault squad come equipped with jump-packs and chainswords allowing them to leap over terrain and get into close combat as fast as possible to rend and tear your enemies into pieces. Should your squads suffer casualties or losses at any time, you can fall back to a relay beacon, which is player captured (similar to a resource point in DoW) and queues up reinforcements to replenish your units.
The main aspect that sets DoW 2 apart from it's predecessors is the Wargear and upgrade system. During your campaign, you'll find different pieces of equipment of varying rarity; green is uncommon, and blue is an item of considerable power that you'll want to equip right away to strengthen your team of marines. The levelling system is where the upgrade mechanic comes into play. As your squads level up, they'll gain 2 points per level which can be inputted to 1 of 4 combat trees, each defining the key strengths and weaknesses of the unit, or maybe rounding their abilities off so the squad becomes more versatile.
The multiplayer in DoW 2 is very enjoyable. I'm not really a PC veteran so to speak, but I've always enjoyed RTS games. DoW 2 has a fairly balanced matchmaking system which utilises TrueSkill to determine what caliber of ability your opponent will display.
I highly recommend Dawn of War 2 to any fans of the first game - it's a great sequel with room for expansions and further campaign extensions.