this game rocks. The graphics are intense. the game is pretty demanding, i can run it on max with my overclocked 8800gts and 4gb ram, but i only average 15-20fps, so i keep it at mid-high.
the single player only covers the space marine campaign, and will take 15-20 hours to complete depending on how many side-quests you do. all of the missions are short, with no save function, promoting proper tactics and strategy. if you crank up the difficulty you should expect a challenge.
This game really shines online. It is pretty much a tweaked version of DOW1, with more RPG features. you can play 4 races online (space marine, tyranid, eldar and ork You need a windows live id to play and there is a ranking and matchmaking system (although it is a little sketchy right now).
I suggest any PC gamer to go get this PC-exclusive ASAP.
(ps it runs through steam, for better or for worse).