The jokes. If it weren't for the jokes, I'd not have waded through the first book. And I still like the jokes, the most recent one that I really liked being the digression by Redcloak and Durkon about relationships with their gods. (Also, without the comic relief aspect Belkar would have just been annoying before Rich finally got around to making him a more than one dimensional character 600 strips into the story)
There was one comic that I absolutely loved that was not jokes - I have a brother who is six years younger than me - it's where Roy gets to meet his (deceased) younger brother in the afterlife.
And almost as good was Durkon's 'reveal' of all of his memories to Durkula.
But mostly, it's the jokes.