The best D&D story since Planescape: Torment, but the camera is still fairly crude.
Mask of the Betrayer is set almost immediately after Neverwinter Nights 2 (probably just a matter of hours). You awaken in a strange cave with a hole in your chest where a shard of the Silver Sword of Gith once was, and the conclusion that your companions are probably dead haunts your thoughts. Just when you think things can't get any worse, you begin to feel a strange hunger. Mask really does a great job at kicking you when you're down, fortunately you immediately receive aid from a Red Wizard called Safiya who believes she may be able to help you thus begins an epic tale.
The story of Mask of the Betrayer mostly focuses around the tragic tale of the Betrayer as the expansion title suggests. It takes a more philosophical approach like the legendary Planescape: Torment, and Knights of the Old Republic II: The Sith Lords, and this pays off I think. While most Forgotten Realms and RPGs in general (NWN 2 included) tell a fairly generic good versus evil story, MotB tells an exceptional story of sacrifice, nature, and resolve. The original NWN 2 protagonist (You can import your old character or create a new one) is joined by a new lineup of interesting characters. Obviously they can't be run of the mill Dwarves, Elves, and Humans since most don't reach epic levels, instead you've got a mysterious Red Wizard, a dream-walking Hagspawn, a rebellious celestial, and finally a Bear God spirit, or evil spirit that absorbs others (depending on a certain choice you make). While the lineup sounds intriguing, I felt that there was a disappointing lack of development. The characters were more intriguing than the run of the mill party members you got in NWN 2, but at the same time you learn the same amount of info as the original lineup... in other words not much at all.
Since the gameplay remains fairly the same I will go over some significant changes\additions. First of all, you've got some new classes and races though I have not used any of them. A good new feature is the introduction of epic levels, you can go from level 20 to level 30 which is nice, but only really necessary for the campaign. I mean, who actually goes above level 20 on the multiplayer PWs?
Mask of the Betrayer's most significant flaw is a flaw that has been around since the initial release of Neverwinter Nights 2. That's right, you've guessed it, the camera. Obsidian made the camera options a little easier to manage by giving you two modes, Character Mode (A more third person perspective like Knights of the Old Republic and Jade Empire), and Strategy Mode (An isometric perspective like Baldur's Gate and a lot of older RPGs). While this sounds good, it doesn't fix the problems. Playing in character mode is often difficult because the camera controls are awful, and if any of your party members are set to "near" in their Behavior follow distance, it can be difficult to see ahead. Okku was a cause of much pain for me, I eventually just set everyone to "Far" so I could actually see where I was going. Strategy Mode isn't much better, while you don't have to worry about party members obstructing your vision, you've got a whole new bag of problems. The controls are once again awful, I don't know why but every time I entered a new area the camera zoomed itself to ground level so I had to zoom out every time. I eventually just stuck with character mode and only used strategy mode when there was a lot of epic spell chaos occurring.
Another important feature added in Mask (and is likely a campaign only feature) is the Spirit Meter. You're now carrying a curse that forces you to consume spirits to stay alive, and there is a gameplay mechanic that reflects this. You'll first get the meter at the end of Act I, and from that point on it is constantly draining. This adds a sense of urgency to your quest, as once the meter reaches certain points it will effect you by decreasing your stats and by damaging you every few seconds, and if the meter reaches zero you die. How you deal with this curse plays part in both the story, and your alignment. You can give in to the hunger and devour spirits giving you some benefits in the long run (but also making you more evil), or you can suppress it as much as possible. There are many abilities you are given that allow you to deal with the curse in whatever way you see fit. If being on the clock bothers you, then you may find Mask of the Betrayer very frustrating at times since the meter drops faster than even I would have liked (especially when you rest). Still, MotB is a better game because of the spirit meter since it adds to the story, and though it can be irritating to manage it adds new challenges to the game.
Graphically Mask is not very different from NWN 2. It features some new monsters and terrain which is very nice, and their quality is at least on par with the original game. Some of the areas are very well designed, but since this is an expansion, it'll feel very familiar... don't let those pretty pre-release screenshots fool you.
The audio of Mask is a significant improvement, I'm pleased to say. Not only has the voice acting been upped in quality, but there is absolutely no music from the original Neverwinter Nights, and Neverwinter Nights 2 used during the campaign. MotB features an entirely original musical score which has both an epic, and dreamlike feel which suits the overall tone of the game very well since the game is epic, and dreams play an important part in the story.
Mask of the Betrayer is an exceptional title. Yes, it still has the gameplay flaws that Neverwinter Nights 2 had, but the storyline and audio alone are more than worth the price of admission. If Obsidian decides to produce a second expansion (mention of the jungle region of Chult implies that they will) I'm hoping that they'll try and surpass what they did with this expansion. Overall, while not as good as Planescape: Torment, Mask of the Betrayer is proof that if given the time Obsidian can produce a title that is complete and above the more big name releases as far as originality and quality is concerned.