A quick note at the start, just to point out that I've run into the author on the writing forum I use (The Write Idea, the link's at the side). I don't think it's affected this review, but it seems only fair to tell you.
Right then, the plot. Harold Waterman isn't the antichrist, but three angels of destruction are getting sufficiently eager for armageddeon to persuade him that he is. He has the right dad, for a start. So they set about placing him in situations to slowly force him to come into his 'birthright'. One of these (an incurable disease) forces him to get in touch with the forces of darkness in the form of the demon Jasfoup, and together they have assorted small adventures, try to cure Harold, and generally set him on a path to evil paved, not with good intentions, but with a combination of wry wit and occasionally vicious slapstick.
Those two are very much the stars of the show here, and Jasfoup in particular steals it as a tea-obsessed tempter of souls, but there's a supporting cast of wierd and wonderful characters drawn with a nice balance between pushing the story along and making the reader laugh. If a couple seem a little arbitrary (such as the sudden appearance of a vampire girlfriend) they don't get in the way and at least serve as springboards for one-liners. Besides, I suspect they'll have more to do in any sequel.
I was initially slightly thrown by the timing of the humour, mostly because one review had compared it to Pratchett. I went in expecting absurdist descriptions and metaphors, when actually, the laughs seem to come in a slightly different way, possibly more akin in tone to Tom Holt. There's a dryness here that, once you're used to it, is very funny indeed.
In the interests of balance, a couple of minor downsides. The copy-editor needs shouting at, because small, annoying mistakes show up here and there. Also the plot doesn't explode at the end so much as about two thirds of the way through, leaving a long-ish ending. Anywhere else, that might have been a serious problem. Here, oddly, I didn't mind too much. I was having far too much fun.