Listening to it a couple of times now, I like that it isn't purely comedic. The comedic bits are the bits describing Christianity as it is; shallow, politicized, controlling. But the overall theme and whole last half of the song deals with the far more meaningful and profound 'reason' for enjoying the holiday: Getting together with family.
As if to take the Christian bits and emphasize just how silly and lame they are by comparison.
I've probably listened to it about 30 times now, over the last week. I liked it immediately, but it also grew on me as being quite profound. It's such an honest song, and it gets to the heart of what Christmas is really like for many atheists. It has nothing to do with religion anymore. That's why it would be so awesome if it made it to the Top 40. It's such a subversive song. Could you imagine if it made it onto a radio station?