There might be a few insignificant spoilers here, so read at your own risk.
There's really not much I complain about in the game, but I recently experienced something that is just bugging me to death for whatever reason. My hunter did Volume 3, book 1 yesterday and I have to say that I experienced the worst thing I think I have ever experienced in my three years playing this game. The voice acting is downright terrible. It actually ruined what is a decent book, though the book is really just running around informing the Rangers that Aragorn is in need of them in Rohan (and Elrond being confused as to why Aragorn went to Rohan).
I'm not sure if it's the same person voicing the instance dialogue that voices Elrond, but that person (or persons) should not be considered for voice acting. The voice(s) just grates on the ears and is nowhere near as good as most of the ones from Volumes 1 and 2. I'm not sure if Turbine was purposely going for a more gruff voice or what, but they succeeded. Though, I'm not sure if gruff is an accurate description. Honestly, I can't really think of how to describe the voice(s). All I know is when this person (or persons) is talking, I just want to go back to having that sound turned off. It was nearly unbearable to watch the movies I unlocked, but I pushed through because I used to not be able to watch any of the movies; the sound wouldn't play properly on my old computer.
Oh, and the 'screaming shadow' from Vol 3 Bk 1 Ch 7 is not very scary at all; it's just the generic yell that characters can do. I was expecting something more since the scream is supposedly so frightening to the Lossoth. This would have been an excellent time to use a variant of Amarthiel's/Narmeleth's scream. (Ha! I was looking at the screenshot I took when I first entered that instance so I could keep track of where I was when I took the other screenshots and I see a nice typo in the quest description; I should go bug that when I'm done here)
On a positive note, I absolutely love the voice from Volume 1; the guy (possibly supposed to be Gandalf?) That does the in-game movies voice and narrates most of the instance dialogues. The girl is really good, as well; I like her voice. The only voice I can think of from Volumes 1 or 2 that I disliked was Mordrambor; he just didn't sound right for the character, especially when he was supposed to be angry and threatening you. Amarthiel's/Narmeleth's grunts were a bit frightening but I really, really loved that scream she did.
Of course, all of this is just my insignificant opinion; yours may vary.