Like just about everything in Final Fantasy XIV, seasonal events are kind of weird. I’m not really sure they should be called "events" at all. They are more like, you know, regular quests.
In most games, a seasonal event is a big deal. There’s a big gathering of people. There are games and activities and daily event quests. There’s a special dungeon or a special boss to defeat. There are special mounts and costumes and occasionally some meaningful gear as rewards.
In FFXIV, an "event" is basically a quest line with a bit of odd story-telling, after which you get a weird bit of costume gear. I’ve done two of them so far. The first was a Halloween event, in which you traveled to each city hub to do a few things, then returned to get … a spooky ghost costume. Actually I got two of them, and they both looked the same. As far as I can tell, you can’t wear them without sacrificing some real armor, because I can’t see where you can setup costume outfits in FFXIV.
I skipped the Christmas event because I couldn’t figure out who to talk to. Then the latest one was Heavensturm, which was refreshing in that it was not at all related to an Earth holiday. (At least, I don’t know of any Earth holidays that celebrate horses.) It takes you to the three big city hubs to talk about the merits of horses versus chocobos. (If you don’t know, chocobos–sort of ridable ostriches–are the default mount in FFXIV and I assume the entire Final Fantasy francise.) There are these folks from "the East" who want to bring horses to Eozera, but they apparently needed an adventurer to pave the way and tell people about the benefits of horses (by prancing around in a ridiculous-looking horse hat).
In the end, you get a mildly amusing mini-story, a handful of ridiculous-looking horse hats, and a handful of semi-neat-looking samuri-style dragon hats. None of which you can wear because you don’t want to take off your real helmet.
Personally I hope this means they’re going to add horse mounts to the game soon. Riding a big chicken is … weird. I’ve seen a lot of white unicorn mounts around but I’d rather have a wider variety of color and style choices. Plus unicorns are for girls. (I’m just kidding! Don’t send hate mail. My character actually is a girl.)
If they do add horses soon, then this little Heavensturm event is a neat way to do it. It’s better than just a patch note that says, "Boom, here’s some horses."