To be short with it, MoB isn't really a sequel to the main game, but a short, disappointing and a little loose expansion
And there is the spirit-eater mechanism SURELY eats you alive, literally and metaphorically. Compared to the main game, the map is too small and the characters that join you are not very interesting like the ones in the past...
Another issue is the difficulty: if you don't find the "rare and exotic weaponry" that gamespot mentioned (I didn't) you will have to cheat or try and try again and again... Rashemen is indeed an epic scenery, but too loose for a sequel to the Sword Coast hero's story, because in Rashemen even the weakest pirate can make the Knight-Captain look useless. So what? You CAN keep training to reach a high level character so you can search for better weapons, right? Right, IF you want to play a boring level-up-only game.
Some say that the game's camera is irritating, but I changed some options in the menu and it turned out that the camera became simply the same one from Neverwinter Nights 2, so I don't see any problem with that.
What I DID liked was that the game has two endings, but that also has a problem for me, because none of the endings were interesting enough so I could be satisfied.
So a lot of things in NwN2: Mask of Betrayer WOULD be great if they were put in a independent game, not as a sequel for one of my favorite games.