I love almost everything about OCaml… but conditional compilation is a minor pain-point I have. I would love to have some more general multistage or “comptime-like” capability… but really, selection of code inclusion on a simple condition would be enough for common needs.
I know I’ve looked through the options available several times over the years, but never anything satisfactory enough that I adopt it. Unfortunately I don’t recall details to have a more concrete argument off-hand.