I'm on the last mission now, and expect to finish the campaign tonight. So far it's excellent, though from the storyline I've been able to get so far it really seems like Blizzard is setting up for a World of StarCraft kind of game after the trilogy is over.
Honestly, I don't think the multiplayer can hold up to how great the variety of the campaign was, or at least not until people get used to the scripting system and create some maps that have more complexity than simply "kill the other player" arena matches. After the success of Defense of the Ancients, I would have thought that Blizzard would have released with a bit more game variety in the multiplayer.