While technically "The Horse and His Boy" would have been the next book after The Lion, the Witch, and the Wardrobe, I can understand why they filmed this one first for the sake of using the same young children. If they had done it vice versa, the children would have aged to the point where they might not look the part as well.
This movie was epic. After the first movie, I had high expectations when entering the theater to see this film. It did not disappoint. They took this to next level. I highly recommend watching this, but only if you have already seen the first or read the books.