[Keeper of Dol Guldur]

On a broader scale, there's a huge distinction between not having any psychological depth and being written so a character reminds you of traits which are found in actual people you know and see all the time in life.

It's important to realize that for the sake of the story, not every facet of each character needed to be analyzed. Especially in a story about a fellowship of people, as we all know in a group, certain aspects commit people to filling a niche in each particular group. A certain group of friends may be described as having a 'smart one', 'crazy one', 'tough one', 'grim one', 'optimistic one', 'foolish one', and so forth.

The Fellowship divided them into those basic parts - naturally the more important characters got a little more depth added.

Also, later on more characters replaced, swapped, and passed on obvious and for the most part clear (therefore being confused for say, "cookie-cutter") characteristics. Boromir went through issues, went a bit mad, died back where he should have been - noble, honest and true. He died, but to take the part of noble, honest and true, soon Faramir got introduced, almost picking up where Boromir left off as far as the quest went.

There were a lot of dynamics that were alluded to also, but which weren't quite as obvious. It's obvious that say, Frodo, has already done a whole lot of maturing . . . he used to be something of a vegetable thief and a ragtag, now he's become a respectable young bachelor.

A lot of minor characters and enemies tend to represent individual characteristics too, orcs and trolls, the nazgul, elves, all tend to represent certain aspects which can be found in all of the characters and in each of us readers too. I think Tolkien, who wrote for himself, automatically assumed anyone else reading would be able to determine various psychological depths without him actively guiding us through their inner psyches.