You’ll be left at the end feeling angry and betrayed because it turned out this was all about belief, all along.
I never "get" those who feel angry and betrayed because a story was "about" something they don't intellectually agree with. If they read the story, and it spoke to them as kiddie agnostics or atheists, then they shouldn't throw it across the room in a rage because it "tricked" them into considering Christianity. What they should be considering is why they liked the story before they knew what it was supposed to be about, and whether the author may have written something more universal than he intended.
I mean, consider the nature of Aslan's sacrifice. Some might argue that it wasn't truly Christlike, because Christ suffered the ultimate doubt at the end ("Eli, Eli...") whereas Aslan went into it knowing perfectly well about the Older Magic. Far from being Christ, isn't he being more like Loki the trickster, or (if we're being really disrespectful) like a lawyer who sprung his client on a technicality?*
What I'm trying to say is that the author's welcome to have his agenda, but that sometimes you have to ignore the author's "agenda" and listen to what the story itself is telling you. D.H. Lawrence had a relevant saying: "Trust the tale, not the teller". Maybe the tale operates on another level than that claimed by the teller.
* Total Devil's Advocate argument, but I hope you can see the point I'm trying to make ;)