We've just published our review of Ossian's Neverwinter Nights 2: Mysteries of Westgate, now that the adventure pack has finally been digitally released. Slight spoilers ahead:
Since Mysteries of Westgate is an adventure pack rather than an expansion pack, it does not contain a lot of frills. It has a new tileset and some new music, but mostly it just includes a 15-20 hour campaign. As the campaign opens up, you learn that your character at some point in the past picked up a strange mask. The mask is cursed -- you can't get rid of it and it causes bad dreams -- and your inquiries lead you to Westgate, where, of course, many mysteries await you.
Characters begin the campaign at level 8, and chances are that they'll progress to about level 14 by the end. You can choose any race and class for the campaign, including the new races and classes from Mask of the Betrayer and Storm of Zehir, but those expansion packs aren't required to play. However, and somewhat oddly, while you can add three companions to your party, you'll only find three companions total in the campaign (a rogue, a fighter, and a priest), and so some races and classes are better choices than others. I played the campaign using a fighter / rogue, and I was consistently annoyed that I didn't have an arcane caster available.