for one if you've read the book, you know that the good guys win.
Don't they in nearly every book that is turned into a movie? I know the Narnia books as audio book adaptations. LOTR of course is a movie so popular and (in my opinion) simply so well done that it is a very high scale for later movies to measure up to. But I think that a movie needn't be as good as LOTR to qualify as good generally.
I haven't seen The Voyage of the Dawn Trader yet, simply because there is nobody with the time to come along to the cinema.
I suppose their concern with the movies was to focus on the books involving the Pevensies but I wonder how they might change "The last battle" in case they are going to make that one. The book received some criticism especially for what is perceived as sexism (Susan no longer being considered a "friend of Narnia" because she apparently has developed love interests). I like the books but they are coming with so prominent a message that one can hardly ignore them.
In this context I kind of regret that another film series based on books is unlikely to be continued. Phillipp Pullman wrote the trilogy "His dark materials" as a kind of response to "The chronicles of Narnia" and those books too (granted, again I know them as unabreviated audio books only) are very interesting. However, the first movie they made ("The Golden Compass") did not succeed well in the US (though it did elsewhere). Which is likely to be partly due to the fact that some religious groups protested against it (while other religious people like the archbishop of Canterbury actually encouraged people to read the books). In any case the one movie they made already had been watered down quite a bit, presumably to make it more acceptable, but in the process I think it lost some of its meaning. Kind of censorship based on religious views and adhered to by economic interests I'm afraid... anyway, I'm getting off topic.