Niggles: how is the base game at the moment?
I just finished it a couple of days ago. The Crown of the Magister campaign is linear and mostly combat based. I'm a little mixed on the way the dialog works. You pick the character to talk/reply and it only gives a brief description of the reply, not the whole reply. In a few cases, the reply was completely not what I was expecting based on the description. The dialog really doesn't affect much anyway. Sometimes what you say will influence your reputation with a faction, or you might get some information that is helpful. Failing a dialog check as far as I know never locked me out of anything, there was always an alternate way. Sometimes picking one character to reply to something has another character say the lines. It was only a problem in one place where the character I picked to reply had a high persuasion skill, but the character that spoke the line and rolled the dialog check on had a low persuasion skill and failed.
Besides the above mentioned dialog bug, the only other bug I ran into was in combat where sometimes it seemed like the game would freeze, but it was the enemy animations not playing and showing the dice rolls. From the patch notes, it seems that should be fixed, along with a bunch of other bugs.
It comes with two other campaigns, but from what I've read they're just dungeon crawls to show off the capabilities of the dungeon maker. I went ahead and picked up this DLC because it sounds like the new story has multiple paths and your choices matter more than in the original campaign.