I don't know if these are worth mentioning or not (from #903, awaiting merge):

The deprecated functions `iris.coord_categorisation.add_custom_season`, `iris.coord_categorisation.add_custom_season_number` and `iris.coord_categorisation.add_custom_season_year` have been removed. Their functionality is available through the functions `iris.coord_categorisation.add_season`, `iris.coord_categorisation.add_season_number` and `iris.coord_categorisation.add_season_year` respectively using the `seasons` keyword argument.

The deprecated function `iris.coord_categorisation.add_custom_season_membership` has been removed, use `iris.coord_categorisation.add_season_membership` instead.

The default names for the coordinates resulting from many of the coordinate categorisation functions have been changed to be more descriptive.