The campaign is pretty damn good (even if the story is recycled from every other Relic 40K game), and I'll be replaying it soon.
The multiplayer is downright awesome... when it works. On the PC it's notoriously laggy, and on the PS3 you can go for literally HOURS waiting to join a game. In fact, I'm writing this as I wait to join, and I've been waiting for a couple of hours now.
All that said, it is worth it, for the sheer pleasure of jumping into the middle of a Chaos Havoc group and hacking them to pieces with a power sword.