I too feel underwhelmed with the seasonal event. Town décor and music is good but it's rather lack luster when it comes to actually things to do.

Here is my wish list of things I want to do and have for seasonal events.

Atmosphere:
City / Outpost should have themed related decoration
Cities should have a musical twist based on the event
Environment should reflect the time of year; fall, winter, spring, summer. Nothing over the top but just a slight change

Event:
Event FATE - event related of course
Event Dungeon - Both lv 15 and Hard Mode
Event Trail - Both lv 15 and Hard Mode

Rewards:
Event themed Minion
Event themed Armor / Outfit
Event themed Chocobo Barding
Event themed Weapon
Event themed Emote
Event themed Items