"Tolkien's experience of war was one of the major ingredients he used in his fiction" Not consciously... Tolkien HATED allegory...

I can't see how those sentences have much to do with each other. Allegory isn't about drawing on your own experiences, it's about having characters and situations that aren't there for themselves and the story, but are there in order to make some kind of commentary on the world.   

Tolkien distinguishes between "allegory" which he repudiates, more especially in relation to his own stories, and "applicability" which is a completely different thing, and which is a characteristic of any good story.

The aspects of the war he draws on don't actually appear to be the fighting as such, but the refusal of comrades to be ground down, and the endurance in the face of impossible circumstances. It was a very odd kind of war, and "the endless meanderings of Frodo, Sam and Gollum" are the part which are probably the parts that owe most to Tolkien's war experience, far more so than any of the battle sequences.   

I'm grateful for Peter Jackson's film, and glad that the extended versions exist as well. I'd be happy to see them in the cinema some time, because sitting in a living room with a small screen is handy enough, but it's just not the same experience as in a cinema.   The whole thing (well I haven't seen the last episode, but I am sure it's up to scratch) is far better than I'd have thought possible. It's just a shame if the ending is a let down.