Was in the middle of Atlantis when the Christmas event hit, so I guess I'll be shifting over to the event.
As for Atlantis, I'm probably about halfway through with it. It has been enjoyable thus far and I've been enjoying the cast of characters. Difficulty does seem easy despite some of the gimmicks involved (although I hear the next part spikes hard in terms of difficulty), so maybe taken as a whole it makes sense for storytelling purposes.
-- One of the things that I find myself needing to do more and more is treating the Avatar as the writer's version of Ritsuka Fujimaru instead of the version I have in mind. This is mainly because some of the choices and dialogue options do not resonate with my version of Gudao (a veteran who saved Humanity during the first arc, and went on more adventures in 1.5). The second arc highlights Gudao's vulnerabilities, which is fine, but it goes about it in a manner that seems to disregard his previous experiences.
As for the Christmas event, it seems like the usual event stuff with the usual enjoyable storyline. While my Skadi isn't fully maxed out yet, I do look forward on seeing if I can do a triple Quick NP loop. If not, I always have options to use Arash and then just do a Double NP run instead.