Thanks to Brockwell.
Got off to a very slow start and was only progressing via "low-hanging fruit" 4-letter solutions, but gradually got on the wavelength and finished in slightly under median Prize time.
Deceptive puzzle: smooth surfaces, non-ostentatious and seemingly simple clues that had many wrinkles and subtleties. For instance 18, as pointed out by rog.
FOI 3, LOI 8.
COD 12 over 6, 23, 24 and 30 (I liked the simple ones).
Didn't notice a theme or bonus features, but a few adjacent across solutions seemed to go together in some sense.