I'll try not to spoil anything in this review, and I'll use very general terms when talking about the story itself (including things not yet in the anime as of December 2020), but if you want to stay entirely unspoiled, this review might not be for you. But the general idea is that Attack on Titan is one of if not the best pieces of fiction out there, and a lot of that hinges on the story post-season 3.

Art: For the first few volumes, I'll be honest the art wasn't very good. At all. But seeing Isayama evolve as an artist is really amazing to experience. Of course even now, the art isn't even close to the level of something like Berserk or One Punch Man, but it's actually pretty good. One thing Isayama does really well is conveying action through chaotic, sweeping lines and sound effects.

Story: The story starts off with a pretty simple premise. The last humans have lived behind concentric walls for the past 100 years to protect themselves from the giant, man-eating monsters (titans) that live on the other side. Immediately this sets up a large amount of questions. What exactly happened 100 years ago? Where do the titans come from? Why are there no records of the history from before 100 years ago? What exactly are the titans? The story takes its time answering its questions, and with each answer, more questions pop up. You get the pieces of the puzzle slowly, but the pieces are entirely out of order. And once the pieces are all in place (or at least enough pieces to make sense of it), there's the question of how the image the puzzle shows should be dealt with. And that's where the story starts getting really amazing, and starts getting more philosophical, talking about the self-perpetuating cycle of violence and hate, and well as differing views on how it can be broken. This is complemented perfectly by the story's characters.

Characters: There are 0 characters in this series that I dislike as characters. Everyone has a role to play, and they all play it perfectly. This series also has, at least for me, the saddest death that I've seen in anime, which requires good characters. The character development is fantastic, with no better examples of this than Eren and Reiner, who move in such opposite directions but at the same time are so incredibly similar, and change massively over the course of the series while still feeling completely natural. That's not something that's easy to do in a story. And another thing that's not easy to do is to have a major conflict with many sides, but to have each side (except for one) actually make so much sense in their arguments that the fandom splits because of it. There are no "bad guys" in Attack on Titan (except for the aforementioned "one side"), just good people doing what they believe is right. And in some cases, they might even be right. It's a story of many different people reacting to a situation in many different ways, but you the reader can understand why each and every character does what they do.

Attack on Titan is ending in 3 or 4 chapters. Isayama showed a rough sketch of the final panel of the series about 2 years ago. I still have absolutely no idea how it's going to end, and there are still more plot twists to come (there's stuff from the first chapter that still hasn't been answered yet). If you haven't read/watched AoT yet, do it.