The problem with that is that I can't recommend reading The Stupidest Angel unless one has also read the previous Moore novels Practical Demonkeeping, The Lust Lizard of Melancholy Cove, Island of the Sequined Love Nun and Lamb: The Gospel According to Biff, Christ's Childhood Pal. The Stupidest Angel recycles characters from each of these novels.
Now, reading those books really isn't essential to understanding what's going on in Angel; the book does work, I suspect, as a standalone. However, there's a "vibe" that the book takes on by virtue of my being familiar with the characters already. There's a subtext, for example, in the somewhat antagonistic relationship between Theophilus Crowe and Tucker Case that one won't realize if one hasn't read the novels in which they appeared before. Not essential, as noted, but still pleasurable.
I found the ending of The Stupidest Angel fairly lackluster (especially in the new final chapter appended in a later edition of the book), as if Moore's inspiration petered out just a bit. The book feels faintly self-indulgent, with all those characters coming back for more, but there's more than enough Moore whackiness to compensate. This isn't Moore's best work, by any means, but it's still a lot of fun to read. Self-indulgent exercise or no, you won't find too many stories out there in which a drunken marine biologist bemoans his disastrous love life with a paraphrase of "The Little Drummer Boy":
I have no sex appeal, pa rum-pum-pum pum.
My social skills are nil, pa rum-pum-pum pum.