OK, we saw it a bunch of times and loved it. Here's what happens:
You go through the queue and end up in front of the Wardrobe (which is huuuge). You spend a tiny bit of time waiting for everyone to get inside. The CM does a little spiel about Chronicles of Narnia being written by CS Lewis and brought to life by Disney/Walden Productions (or whatever they're called). The doors of the Wardrobe open and you walk in to find yourself in a forest full of snow laden trees, the lamppost and Mr. Tumnus's house. It is just like you're right in Narnia (and walking through the Wardrobe makes it seem even more so!). Then, there's Liam Neeson doing a voice over about the basic premise of the story ... then the spotlight hits the White Witch, who walks across a walkway at the top of Mr. Tumnus's house. She lip-synchs the small speech the White Witch gives about "If it's war Aslan wants, war he shall have ...". The actress looks just like Tilda Swinton in the movie -- same costume, hair, etc. Then, she goes off "stage" and the front screen (which shows the area to the White Witch's castle) turns into clips from the movie w/Liam Neeson doing more voice-over. After the movie clips, the spring tree comes alive and you are ushered into an area which holds the White Witch's costume, Lucy's dress, the White Witch's carriage and wand, the frozen people props from the movie and a couple of other things. You can spend as much time there as you want to.
I am a huge Narnia fan and so is DS9. Come to think of it, Daxx got pretty into it, too. We loved it and thought it was neat to be in part of the set!!!!
Anyway, I think most people (even those who haven't seen the movie) would enjoy it. There's nothing scary about it and even if you don't know a thing about Narnia, you'll get a sample of it.
One guy in front of us said "This was just one big commercial!" when it was done. While he might be right, we all thought it was fun to be in the set and to see bits of the movie as well as the costumes and props.
ETA -- they really don't show you any "movie making" techniques or go into details on how they came up w/things. It's a less-than-15 minute thing ... so if you're waiting between fast passes, this is something to consider. When we were there in Jan., we never had to wait more than 3 minutes in the queue to get in.