Neverwinter Nights 2: Mask of the Betrayer

The Good
Unlike Bioware's somewhat predictable expansion packs to NWN1, Obsidian takes us by surprise in Mask of the Betrayer, reinventing that very commercial genre of RPG add-ons from the ground up, and giving us something that is qualitatively and experientially quite different than 'vanilla' NWN2. They're having so much creative fun with their engine, it's a joy to behold.
We are introduced to the concept of spirit-eating, which ends up to be pretty much more than a gimmick or a mere plot point: it partially replaces the fundamentals of the NWN2 mechanics, so that the hero's mysterious affliction becomes the driving force around which everything else revolves. They intend to convey that spirit-eating is not just some fancy RPG "augmentation", but a pervasive condition that both governs and threatens much of the character's running emotional and mental life. And they succeed with flying colors. It lends the add-on an existential and even "alien" feel when compared to NWN2, and everything feels more urgent than in either of the more conventional expansion packs to NWN1.

I gushed about creativity in an earlier NWN2 review; well, this add-on has a creativity overload. To call the plot, the juicy dream sequences, and many of the conversations poetic may be too big a word, but it is close.

The Faras-Enzibur sidequest in particular, a very detailed account of a wizard's contract with an insidious devil, is a gem of intricate writing. As a budding writer, I've sure read (and most probably wrote) so-called literary short stories that are far less intriguing and worsely written. I've also found the Anya-Gann sidequest memorably endearing despite being very short. It takes skillful and imaginative writing to set a quest within the dream of a lovesick farmer girl who transforms into a dragon in a naive attempt to protect her illusory loved one.

Again, the colorful tidbits: the tiny, overlapping "subquests" in the Skein and in the Ashenwood, all with lively dialogs.

The Bad
Criticism of the NWN2 engine and overall gameplay scheme obviously applies to its add-on as well, but if you've played through NWN2, chances are that by now you've at least made peace with the engine. It's still "hands-off", there's not much to explore in the Gothic/Risen sense, but the Aurora Engine is taken in new directions the original NWN2 couldn't dream of.

The Bottom Line
Mask of the Betrayer is a relatively short but sweet experience that, through its gameplay innovations and flawless writing, injects new life into the very framework of Neverwinter Nights 2 which, in turn, was such an improvement over the comparatively stale NWN1.

When taken in isolation from the main game, I regard this add-on as the single tightest and most exciting adventure of the official NWN1-NWN2 canon. It's also the weirdest and most disturbing one. Mind you, that's a compliment.