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SasqWatch
GameSpot's review of Mask of the Betrayer criticises the spirit-eating mechanism and camera but praises the choices and puzzles, calling the expansion "mature". The score is 8/10 and here's a snip:
More information.The expansion also does a great job of diversifying the gameplay. In NWN2, there was almost no situation that couldn't be solved with a little combat. On the other hand, Mask of the Betrayer is packed with all sorts of devious puzzles. For instance, a trip to a wizard school will have you trying to figure out an elaborate mirror puzzle, as well as attempting to break a contract with a devil. This is an expansion that will make you think, and that's a good thing.