Honestly, it's a bit hard to determine how good or bad this series is as of now because, at the end of the day, the ending is just as important as the story itself and there are many loose ends that need to be tied up and if they are not, then this manga might just drop to a 7/10.
As of now, the story is good and it makes perfect sense upon reading all chapters twice or even three times. You can see how things progress, the small foreshadowing, and the threads being left open throughout so any development can be expected if you see the small details.
The art is good but a bit rough, the characters are distinguishable from one another without much effort even though all are using the same uniform most of the time which is great. Some details get lost along the way because the lines can be a bit rough sometimes but overall, it's really good.
The character development is also incredible. Almost every single one of the characters has a character arc except some of the side characters and Armin but it's compensated by Eren's arc which is incredible and really understandable.
I've been enjoying it a lot for a while now and I'm sure many others will if they can handle the sometimes slow pacing.