I think Targon suffered a lot from being hyped as an "event" sort of thing. That rumor sorta started who knows when, and people were excited for Burning Tides 2: The ReBurnining. But it...wasn't. And the thing is that it was never supposed to be. Jaredan even explicitly said it wasn't an event in the way Bilgewater was. So that really satisfying storytelling that went with Bilge wasn't present.
Targon was more of a round of Lore updates, and a new champion coming out. There was no real progression on any of the character stories, and although we learned more about Targon, I'd call this more like what happened with the Shadow Isles last Halloween. It's a lot of updates for characters, but no plot forwarding for them. This is kind of a classic "Old" Event for League, like with Freljord and Shurima, where a lot of conflict is set up, but nothing is yet resolved, unlike with Bilgewater, where things did get resolved, especially with regards to TF/Graves and MF/Gangplank.
That said, I'm still excited for the next "full fledged" event. Burning Tides was fantastic.