While reading CONUNDRUM, I honestly couldn't tell who had the most fun -- the reader or the writer. Most of the jokes that Steve Lyons comes up with are of the type that instantly provides us with an image of the author racing through pulp and dime novels gleefully looking for conventions to subvert. One imagines that he also rewatched and reread several earlier Doctor Who adventures, as there are one or two knowing winks to standard formulas.
What starts off as a relatively typical murder/mystery/vampire story (they're more common than you think), thankfully, becomes a much more bizarre tale. "Thankfully", because a) the original story isn't all the great to begin with and b) the tale that follows makes the beginning portions of the book much more interesting and (more importantly) funny in retrospect. The humor is very clever and is never anything less than charming. It makes the entire story engaging and engrossing. In many places the plot is secondary to the fun, but since it is undoubtedly effective, there's no problem with that.
There's something about Steve Lyon's prose that I find really appealing. It's not especially poetic, but there is a certain flair to the writing. It has the quality that makes it appear to have been effortless to write; whether this is true, I don't have any way of knowing, but it's certainly effortless to read. The characters are all deliberately a bit vague and stereotypical, but this is obviously done on purpose and Lyons plays a lot with the audience expectations.
One of the more enjoyable NAs in the series, CONUNDRUM has held up very well since its publication. A handful of later books would attempt a similar breaking down of the fourth wall, but none of them would be as entertaining. A great book, and one that kept me guessing all the way through.