The story itself is really good, super interesting, and super evocative. The switches in perspectives between the two protagonists is very emotional. This isn't a show that focuses on the action, it's much more focused on the experiences of people from two vastly different backgrounds, interacting with each other and working together in a bleak, seemingly inescapable situation.
However the execution however is pretty naff. The themes don't feel like they're adequately explored and are just kind of lightly touched on or kind of ignored (more so in the second half). Besides one specific theme of the show, they're not often engaged with in a meaningful or thought-provoking way. It feels like a lot of the storytelling could be far more succinct, and often the conversations feel very unnatural, like they are just giving exposition or outright stating their moral positions rather than it showing through their actions or through subtext. The characters spend a lot of time on screen but it doesn't really seem to build their personalities adequately or do much work to really endear you to them. Motivations for some are unclear (which works for one of the main protagonists), however some other characters motivations stop making much sense at a certain point because their reasons for continuing to do what they are doing just isn't really fleshed out. I like when an anime doesn't rely on the trope of inner-monologues too much to tell a story, but it feels like in a lot of cases in the show, it's warranted. A lot of emotion is lost by not being able to see inside their heads. The two main characters are really the only interesting ones to watch. Essentially, there is a LOT of telling rather than showing.
The first half of the series could do with a good 50% of the run time being cut down even though it is the strongest part of the show. One of the key aspects of the story comes across rather silly in it's explanation which I can forgive for the sake of the stakes and tension. It often feels like the score by the legendary composer of Attack on Titan is unearned when it launches into it's big moments. If you're a dub watcher, you may be disappointed. As someone who usually watches dubs, I would definitely say that this is one to watch in Japanese. The dub's performances in this show just don't really land the majority of the time, and the adaptation to English doesn't seem like it was done with much flair.
Still, I'd give it a go. In spite of exploring similar themes, it's no Attack on Titan, but we can't fault an anime for being unable to match up with one of the greatest of all time.