I rented this film the other day having not read the books (or heard about them at all).
My choice was based on the cast (Tim Robbins, Martin Landau, Toby Jones and Bill Murray amongst many others)- I'm also a fan of fantasy/magic/escapist stories.
I was NOT disappointed. The cast was predictably excellent, in particular the two young leads. The story itself was unoriginal in its premise but gripping nonetheless.
Most of all what made the film for me was the strange city of Ember itself. I loved the idea of an underground city depending on its generator to survive. It was visually a lovely film and the last few scenes were very moving. Oh, and the voiceover was perfect.
As far as the beginning being slow- I didn't find that at all. The beginning sets the scene for the story to unfold and introduces the viewer to the city- the mayor, the way the kids are apprenticed, their day to day life, their job etc.
All in all I was hooked and am now in the process of buying the books!