As someone who's read the Silmarillion, I still found the movie enjoyable, despite the complete omission of vast tracts of historical dialogue from it, maybe I wouldn't have enjoyed it as much if I hadn't.
I'll agree that some of the alterations made to the major battles irked me a little, but the thing is, the story was more an interpretation than an actual word-for-word conversion.
I'd have liked to see some more cleaning up at the end, more confirmation of the friendship between Gimli and Legolas in particular, and the fact that Gimli established a new Dwarf-Home in Helms-Deep, and then became the only member of that race to travel West, because Legolas refused to leave Middle Earth without his friend, I think that would have made a better ending in a way.