Though I still don't agree with Lewis that his point of view, his conclusion is inevitable and the best answer to the question of the original of morality, I think my main problem with the book so far is that it's not what I was led to believe it was. Everyone recommends it as this great work of Christian apologetics. They treat it as convincing. It's not, at least I haven't found it to be so far. If you're approaching the questions it addresses from a Christian point of view, it makes perfect sense and is logical to a certain point. If you're looking at it from outside of that mind frame, the arguments he raises are either no more or less valid than other arguments for other points of view, or they seem antiquated and incomplete - not through any fault of Lewis' really, but because we understand the human mind so much better than we did in his day and age and the drives that move us.
I took a few days off from the book after I finished the last two chapters of the first section and that's the conclusion I reached. I'm planning to do a post covering those two chapters tonight and then we can move on to the second section which is supposed to be about what Christians believe.