Flaws in Lord of the Rings... Yes in the book.

[Imladris]

I don't understand why you say that LotR is flat and two dimensional and simplistic? If you think about it, that is what life is. Either something is bad or it is good. There are a few shaded areas in the details of life but ultimately there is good and evil.

But the underlying sense of good and evil is still the traditional and conventional sense

Ultimately, there are very few different story themes and the theme good vs evil is the common one, I think. Break any story down and you have that good and evil there. What makes a story stand out is the way it is written and I haven't found anything as detailed and intricate as LotR...Tolkien re-defined the meaning of elves and created a mythology for England.

I really don't believe in absolute evil.

See, that's where you and Tolkien disagree. Tolkien was a Catholic (which is similiar to Christianity in some ways) and he probably did believe in an ultimate evil. Even though he protested that LotR is an allegory, his world view definitely crept into his story. It's a personal issue there.

Cheers!
Istawen