I enjoyed this movie quite a lot. The story line would be hard to follow if you had not read the book or at least have seen the other Narnia movies. This is very typical in a sequel.
This movie is definitely for Harry Potter fans. The movie assumes that you already know the main characters. So... READ THE BOOKS, and then see the movie. My only complaint about this movie is that it doesn't show how deeply and selflessly Harry loves Ginny (the books delve into this).
As for the ending, I couldn't imagine a better place to stop, or pause the movie. I believe that most of the frustration that people have expressed is due to it being only part 1 of a series.
Criticism of the "nude" scene are greatly over-exaggerated. If your kid is old enough to love Harry Potter (all of the books), then this shouldn't stop you from taking him/her.
Has the classic good vs. evil. You'll fall in love with Pandora (their planet). Watching this movie was like eye candy. Although this movie is long, it didn't feel like it. I liked it so much I'll buy it on Blue Ray when it comes out.