What always makes me happy is knowing where I can find Thancred, and also rewatching his cutscenes. As such, 3.1 was literally the best thing to happen to me lately in the game. Not only is Thancred back, but he's back in style, and he proved he can hold his own against a Warrior!
Krile was also a delight, and so was finding out that we know where F'lhaminn, Hoary, Yda and Papalymo all are, and that we're likely well on our way to finding Minfilia soon too! Being back in Rising Stones with Thancred and Krile is so relaxing, and the great new idling camera has some beautiful shots in there.
Other things that make me happy: among other players, there are a few whom I can trust and who are so fun to hang out with or just PM. Minions: those are always fun to collect, but I just wish that the MogStation ones would go to all your characters instead of just one of them once you've paid actual cash for them. Mounts: I just love flying around on Midgarsormr, or riding either the Manacutter, my personal Othard blue chocobo Zack or my draught chocobo. I also love getting new achievement items whenever I can. I'm also strangely in love with the Think emote, it looks pretty great on female Miqo'tes. In addition to the above, I just generally love rewatching MSQ cutscenes every once in a while. Really, the game is nothing without the story. And finally, I just love listening to the beautiful music of areas like Rising Stones/Waking Sands and Matoya's Cave.
With regards to 3.0, pretty much the only things I liked were the few good bits of music that it had, the few good Elezen NPCs that we interacted with, all of the dragons in general (including Nidhogg) and Ysayle. The rest of it can go screw itself, cauz it was annoying to blunder through quests and bounce back and forth between Ishgard and the rest of Eorzea. Really the only good thing that came from 3.0 was that we got Y'shtola back, but generally speaking, Ishgardians are annoying and their wintery weather sucks.