Since you're asking... (and bear in mind I do not agree with all of the following points...)
1. Lingering resentment over 6.0 not meeting expectations. (The "Endwalker SUCKS!!!" thread over in General is still there... with people still complaining... almost 2 years later...)
2. Bad pacing.
3. Trite, shounen "power offriendshiptrust" lesson.
4. Rough if not outright bad dialogue at points. ("That was what possessed me," indeed.)
5. No shakeup of the status quo (re: "consequences").
6. Leaning so heavily on IV fanservice for the MSQ.
... and the fact Dawntrail is shaping up to be a fun adventure instead of dark and gritty has the same people so critical of Endwalker very nettled, which isn't helping matters.
The worldbuilding around the Void was interesting, and Golbez and the Archfiends were good characters... but the rest was pretty terribad, to be honest.