I caught the late show of Narnia last night. Paid full price. Worth it without question.
The unfortunate thing for Narnia is that it will inevitably be compared to Lord of the Rings. It can't quite stand up to that comparison. The main difference is that the Narnia stories are really intended for children, whereas the LOTR tales are written without an age group in mind. Thus, Narnia doesn't carry the same terrible feeling of impending doom or massive relief at the escape from doom.
One of the primary factors that makes Narnia so much less threatening is that we see so much of the villain, the evil queen. In LOTR, the ultimate villain is always beyond our grasp. So ancient, dark, and terrible, one can only strive in near blindness to prevail on faith. Here, the Queen is bad, but quite manageable by comparison. Like I say, Narnia is a children's story. They can't handle as much. In a way, Narnia is like The Passion of the Christ if you tried to make it endurable for kids. The result is entertaining, beautiful, reverent, and something that adults can enjoy, but is not FOR adults.
My distinction between what is for adults and children would possibly not hold up so well in an age where adults were not as world weary and jaded as we are. I suspect an audience from an earlier time would have all the violence and threat they would need to be pushed to the max by this film. That may be part of why C.S. Lewis wrote for children. They are still impressionable and in a good way.