I wish you luck with Lewis (he's probably in the family somewhere, and he deserves all praise for his other literary achievements), but the Space Trilogy is NOT in the same realm of brilliance as Narnia. I almost never put a book down once started, but I could only get about half-way through the second one.
He actually wrote these some years before TLTWATW; he was not mature as a writer of fiction, and it shows. Unfortunately, the vast success of the Narnia books made ANY 'popular audience' novels by Lewis popular with publishers and booksellers, otherwise I think these would have faded away.
hmm well... that's kind of discouraging. still, i spent almost a year waiting for the whole series to be available at the library (i just couldn't justify placing a hold on them, since i wanted them for pleasure, and someone else may have been using them for research).
well, at least there's this: Narnia was a quick read, so if these are less developed, hopefully I can at least plow through 'em... i guess i'll find out.