Turbine did with this game what Peter Jackson did with the movies.
The main quest-line, and most side quests are artfully told, and presented in such a way that one quickly gets the feeling that something big is happening in the world, and you want to be a part of it.
While many other mmo's tend to have scenery that's decoration only...not meant to be explored and often blocked off...everything I have come across so far I've been able to get up to and run around in. Ruins don't have that "randomly placed there" feel, but rather have a feeling of historical belonging, of purpose long lost in time.
A couple of the negatives for me are that the UI is a bit awkward at first, and crafting can be a bit confusing for beginners.
The community is top-notch, being the most helpful and mature I've come across.
Were Tolkien not so against modern technology, I would think he'd be pleased with this portrayal of his creation.