It's a big budget movie with great staffs and voice cast. It had lots of hype, maybe that's a reason why it felt more disappointing.
Anyway, let's start with the good parts.
Animation: Just mind-blowing. I don't have anything else to say.
Voice Acting: It's not bad. It had a mixture of great veterans and rookies. And they did a good job.
Music: It's Sawano Hiroyuki, and he did what was expected from him. The opening and ending songs by Eve and riria was great. I'm a fan of Eve I'm more than satisfied with the song. And riria's voice is also great.
The bad part is the plot. The one in charge of writing was Urubushi Gen, who is undoubtedly one of the best out there in the industry. But he did a rather underwhelming job here. In the middle of other great parts, the bad writing stood out more. The plot had no explanation or any proper backstory. Just some supernatural things happening without any reason. The characters had no developments at all. The female protagonist literally had nothing in her. It wasn't even explained what she actually is.
The main problem is no questions were answered. Why, what, how- nothing at all.
In conclusion, if you're in the mood of watching something for cool animations, great visuals and score then I absolutely recommend it. But if you are like me, searching for a good story then don't watch this movie.