I didn't vote in the poll, as my answer would be "The writing is excellent, but..."
I first read the Narnia series when I was 11, and enjoyed them immensely. Although I had read fantasy before that, I hadn't read anything quite like that series. It definitely left a lasting impression on me - I have a persistant soft spot for talking animals, and some of the morals of the stories stuck with me and helped to form how I see the world.
I didn't see the allegory in it at all when I was a child; Christianity pretty much rolled off of me like water rolls off of a duck (despite my poor granny's best efforts, heh). When I re-read the series a few years ago, however, the allegory made me quite uncomfortable, especially as it felt quite heavy-handed. Being more aware of the world, I also felt very uncomfortable at how all of the 'bad' people seemed to be dark-skinned, which is put across in a way that makes it more painfully obvious than when Tolkein did it.
All the same, I still love the books - allegory aside, there's a very good story in there and some very good wit. I will always grin when I come across the line, "There was a boy called Eustace Clarence Scrubb, and he almost deserved it."