The series itself has had an interesting concept since the very beginning, but the final season did a job one can only bow down to.

When I first watched Attack on Titan, I was not that much into anime, so I was a bit appalled by the show during the first season: To me, the concept of titans running around and eating people was just strange, and the show was at season two, so the hype was not really there. A friend forced me to continue it, and it is now one of my favorite shows ever! The plot seemed to be a bit slow, but I understand that that's a world-building thing. Many of the things that I disliked about aot later became things I appreciated (like the slow pacing). 
So if you are currently watching the show and don't know whether to continue, please do, because the plot, animation and world-building are only gonna get exponentially better.

Which brings me to the final season. This season is without a doubt the peak of this anime.
The switch of the point of view at the beginning of the show had me so invested. The plot points were all so well done,

Spoiler, click to view

!~I got literal goosebumps throughout this masterpiece of a show and a season!!!! The moment where Eren and his father are in his memories had me on pins and needles; it was such a crazy twist. What is even crazier to me is the fact that this was all planned in the previous seasons and that you can see Eren and Zeke in some scenes?!!!! ~!

The conclusions each character got individually were so fitting, especially when it comes to the main cast: Eren, Mikasa etc. (I loved Levis as well, but it did not hold as much of an impact). 

Spoiler, click to view

!~I do want to say that Eren gets criticized rather often, but in his mind, I believe there was no other way. He did admit it was selfish, and he did not wish for that ending, but Eren stands unchanged in the entirety of the show. He was that angry child striving for freedom, and he still is. Eren as a character just shows the tragedy of the show, and the author made a point by having Eren stay the same.~!

Of course, the total conclusion of the series itself was great too, definitely better than in the manga. For the manga readers, I do have to say that a decent amount was changed, but this does not ruin the manga or the anime; I'd just see them as two different works. I really disliked the manga ending but enjoyed the anime one. Although the manga did convey the tension at the end better in my opinion, it was just not as well-rounded as the anime ending was.

The music is great as well; I got the OST of Mikasa fighting the Warhammer saved in my favorite songs. Natrually the animation was great too, and the direction was phenomenal; the scenes were all so well-thought-out.

I was annoyed by the whole part 1, 2, 3 thing though. I remember when it came out: my friends and I were so hyped about the final season, only to find out that we had to wait for part two and part three. Of course, the anime and story weren't worse because of this; it was just something that irritated me during the release dates. So I am kinda jealous of the people who do not have to wait a week for the next episode or a year for the next part.

They did a fantastic job, and I could not be happier. ^^