Being a long time Tolkien-gaming fan, these are the four points that I always seem to stumble upon when I visit LOTR-forums.
1) Flashy Magic: A concern that has popped up on most LOTR forums that I've visited. Magic in Tolkien-based games should be rather subtler than it is in other universes (Elder Scrolls, Arcania, Dragon Age, ... ). The universe is expanded enough to allow some freedom (the half-Wraith creation being one of them) but just don't push it to the limit with flashy effects and a complete dependance on the use of magic. The real magic in the Tolkien-universe is the strenght of one's persona, whether it's driven by courage, love or revenge.
2) Middle-earth or LOTR? It's subtle, but it is there. This is the first Tolkien-based game that does not contain "The Lord of the Rings" in it's title. While I applaud this decision to dive into the universe beyond the books and films, I really hope there will still be ties to the universe most of us are familiar with. However, please DO NOT just add characters we all know just to prove how much lore you know. Yes, everybody likes to run into Gandalf or Elrond, but when you run into them in Mordor, they'd better have a good reason to be there. The lore should be interwoven into the game world. Players shouldn't have the feeling that they step outside the world for a couple of minutes to catch up on the lore. It should be part of the world they're exploring. It'll greatly augment the immersion in Middle-earth, which hasn't been thoroughly done before.
3) The Curse of LOTR AAA games: I've been around on LOTR forums since 2006, and I've noticed something that I would like to call "The Curse of LOTR Triple A-games". It started with the first Triple A-project I decided to follow: The Lord of the Rings: The White Council. It was a very ambitious project, but somewhere late in development EA decided that they wouldn't renew their license for LOTR gaming and they dropped the project early. Instead, they rushed Pandemic's LOTR: Conquest to be released before the end of the license. The game was not able to receive the necessary post-release attention because Pandemic was disbanded and EA had to shut down everything LOTR-related (see also: forums and online servers for Battle for Middle-earth) because now Warner Bros. had bought the license. They decided to go with LOTR: The War in the North for their first LOTR Triple A-game. After WitN was released, Snowblind Studios too was disbanded and merged with Monolith Studios (of which the devs will undoubtedly know more). This however resulted in another lack of post-release support. The result for Triple A LOTR games is mostly the same: a decent game that is well-liked by fans, but that lacks the necessary post-release support.
4) Action vs exploration: Action has always been the focus of LOTR games. This wasn't bad for the movie tie-ins and War in the North, but it lacks an important aspect of Tolkien Literature: exploration. It's the same important reason that the Middle-earth Role Playing Project [A PC mod for Elder Scrolls IV: Oblivion and later for Skyrim] got so much attention. It would have been the first game that would allow you to roam and explore the vast world of Arda. Since this is the first free-roam game set in Middle-earth, I expect this aspect to be far more developped than in previous games. Not every corner of Mordor should be filled with action. Sometimes an open world should just be beautiful to explore, as was Bilbo's reason to get out of his Hobbit hole and follow those Dwarves. A game that did this very well, in my opinion, was Red Dead Redemption. The vast plains and hills were desolate and forsaken of life at some times, but it suited the story so well that it actually worked. When recreating Mordor, Middle-earth or any other region, the background of the region should be taken well into consideration.
When all goes well, and I'm certain it will one day, then we might be a step closer to the perfect Middle-earth game.