Can't say what other people dislike about it, they have to answer that themselves. For me the most disappointing thing was the story, the second disappointing one the white mechanic markers on an almost white background. They're very hard to spot in time with bad eyesight.
I haven't played any NieR game, just heard of it, but I was intrigued about Automata, because that postapocalyptic stuff is something I usually enjoy. That's why I was looking forward to that raid, hoping it would give me an idea of how the actual games are. And then the raid made me feel like a bystander who's only good for fighting. Whenever a question arised, none or only a very brief answer was given. All the NPCs from NieR were doing a "just trust me", "can't explain now, the bad ones attack" or "I'll explain once we're done". But nothing ever came apart from vague hints. The dialogues with the dwarves were funny where they pointed out that your replies didn't matter until that's what was actually how the raid in total treated me. We were supposed to follow blindly, only getting just as much information for a general overview why this raid exists, and when everything was over, everyone who could have added more depth to the story disappeared for the greater good. I suppose a lot of that made more sense or be like "but that is so obvious that x happened because of y and a is connected to b" for people who played NieR, but.. I haven't, and a collaboration should make the game enjoyable for fans of both franchises.
Then the post-raid story started and again it had interesting points that looked like they would add more substance to the plot, with Konogg's messages and the suspiciously acting dwarf. But the strange things in the village were dropped and the end was an open end where most "what could've happened" scenarios painted an extremely grim future for Konogg, or no future at all. And endings like those feel unrewarding for me in general, but especially here considering that the game didn't even let us help at all and more or less killed Kanogg off, metaphorically or literally, who knows.
Of course there are some open threads in FFXIV, too, but this is more about a storytelling where you like to have a few options for elaborating further or connecting some dots at a later point, like in a tabletop rpg. The most important things are addressed and explained eventually. This raid was a big puzzle with 10000 pieces of which you get 100 unconnected ones as an excuse for fighting.
I guess there is one positive thing about it though: Afterwards I looked for the internet for answers to see if I might have missed anything due to my lack of knowledge and all I found were posts saying "That's just how NieR storytelling is". So the raid helped me indeed with my decision about playing NieR. Now I know I'll keep my distance.
Hope that helped.