Since we're talking evenrs and we approach the first repeated event, how about we rank them so far, worst to best:
Summer Games 2016
I agree with Veelk that this the least interesting event conceptually. That's not to say the skins were all bad, but I wasn't that fussed about missing out. Admittedly I didn't play Lucioball to properly judge it, but I'm not too enthused by its return. The menu music was pretty good.
Overall it was just okay. I hope the 2017 iteration at least spruces up one of the maps. A new Brawl alongside Lucioball would be great too.
Overwatch Anniversary
I feel a little harsh for putting this second last, considering that it brought three new Arena maps, some great dance emotes and an assortment of cool skins. Unfortunately the event-exclusive stuff - the emotes and skins - were really all there was to it as an event. No new Brawl, no prettied up stage etc - it all felt a little lacking as an event.
Hell, even the main menu screen felt a little lacking, even if it was cool to see all the heroes together. It was too far away to really get a sense of anything. Some smaller group screens migbt have been better. The menu musoc was okay, if a little generic. An okay event.
Lunar New Year 2017
This was a good'un, with a great collection of skins, emotes, highlight intros and a Capture the Flag mode. The additional bells and whistles to Lijiang were nice, but it was odd that they were limuted to the CTF mode. The menu music was really nice too.
What knocks it down is the CTF mode. While fun, the mode essentially encouraged camping on the flag and letting Sym, Torn and Bastion clean up. This meant that attacking was discouraged, which led to a lot of draws. CTF to this day still feels a little crowbarred into the game.
Winter Wonderland 2016
This was a great event. There were some some great skins here, and the Widowmaker misletoe intro is incredible. I absolutely love what they did with Hanamura and especially Kings Row. The latter especially really nails a Dickensian vibe, and the payload sleigh is a treat.
The Snowball Offensive was a little frustrating, but Mei and 76's dialogue made it worthwhile. The menu music is my favourite of the bunch. Honestly the only real weaknesses I can think of is that a couple of the skins - Mei's legendary in particular - aren't worth the coins.
Overwatch Uprising
The firsr true lore event and it was a doozy. I really enjoyed the King's Row mission, and liked the interactions between the four heroes as you went. Getting a bit of insight into Overwatch before everything went to shit was cool. I also appreciated that you could play the mode with any hero separately. The skins were mostly fantastic too, with Blackwatch Genji being a highlight.
I can't really think of much wrong with this event honestly. It was just solid all over.
Halloween Terror 2016
The best of a best. Awesome skins, awesome PvE in Junkenstein's Revenge, an awesome night version of Hollywood - just fantastic all over. They'll do well to top this come October. Give me Bride of Junkenstein!
Just, for the love of God, make the menu theme less grating after a while. Please.