I think there should be seasons, and snow and leaves fall as the months change.
That would be nice. And along with these changes, there could be varying forms of creatures/wildlife seen
more or
less often due to seasons. In winter, your character could mumble a complaint about freezing cold water (because really, who just goes for an arctic swim...in full combat gear, even?) Maybe some potions could randomly freeze, unless you say the "magic" in them prevents that; NPC's could definitely mumble cold weather complaints as they go about their lives; travel services might be a little slower in the cold, ships could minimize movements due to storms and icy conditions, etc. And there should be some health penalties for running around in obviously cold conditions when barely dressed.