I had a lot of fun reading this manga honestly. The artwork at times was just downright amazing, and I think what stuck out to me the most was probably the characters.
My biggest praise for this manga is how the characters were written and how you got to learn more about them later on. Also, no matter how you actually feel about the series is, you have to admit that they all look pretty original from characters from other animes (like sao with all of the characters looking really unoriginal in my opinion...)

Now... here are my complaints.
The ending felt SO rushed, that it just made me feel sad. The series that I had been enjoying for over a year felt like it had been wadded up into a ball and thrown into a dumpster fire. If they would have added more of an explanation to what happened to all of the main characters in the end I wouldn't be saying this though.
Also for people who start the series, I could understand why it can be hard to actually get into it because the plot is REALLY slow in the beginning.
But of course, that's the beginning, and that clearly changes after awhile.

So to all the people considering to start it, maybe keep these things in mind, and also just keep reading through it, even if the plot can kinda be a bore at first.