Well, after putting it down in a fit of pique when I thought it was a Harry Potter themed crossword, I picked it up again this morning and really enjoyed it. I'm embarrassed it took me so long on my LOI (16d) to work out the parsing, but I thought for COD the clever 12a vied with 23d, which I believe is a reference to a marvellous episode of Inside Number Nine.
Only answer I still can't parse is 18d.
Thanks to those who encouraged me to take a second look.