Fully agreed.
Hats off to Brockwell for a brilliant (trademarked) thematic construction.
Fortunately I saw the theme early, and it helped greatly with solving, but I still rank the puzzle on the difficult side. Enjoyable time well spent.
FOI 5, LOI 7 which required Google for unknown GK.
Many of the thematics were COD worthy.
I'll go with 6 as my somewhat arbitrary COD. Others of note: 18, 13, 9, 23, 12, 13 and 8.