I just want to convey my personal thoughts before the current years runs out.
Honestly, when the last chapter (finale) was released way back on April I felt a sense of personal fulfillment, since Isayama-sensei tied all plot knots and closed every character arc in such a satisfactory manner that I felt no need for a sequel.
It is clear that AOT amongst its many themes carries on one that is particularly nihilistic, that is regardless what mankind does or not life moves on without waiting for anyone or anything, because in the grand scheme of things humanity (like any other lifeform) is insignificant. Proof for that statement can be found in the closing pages to the expanded ending released within the last tankoubon back in June.
The evidence, the rest of world waged war of retribution against Paradis a hundred years or so after Eren's death. Although civilization in Paradis was razed to the ground, the flora and fauna not only persevered but also flourish centuries later, as depicted by the General Sherman tree that grew uncharacteristically humongous.
Like others previously posted the story went on a cycle that was intended never to be broken no matter how hard detractors attempted to sway the players with logical arguments to avoid repeating or paralleling the mistakes from previous generations.
Just like in nature that natural phenomena and cataclysms come in and come out ocasionally, and there's nothing that man can do to at least avert them.
In spite of all, I honestly believe that AOT was a believable and well executed story with relatable characters and good, written ones (a.k.a. orphan Ymir's story arc).
It is a story that on surface takes on the basic elements and tropes of a traditional shounen genre, but inside out deconstructs them in order to flesh further its characters so that we readers may be able to delve deeper into their psyches.
For a personal note, the most memorable moment for the last chapter that made me cry manly tears:
Immediately after that, the second memorable moment to me happened:
All in all, even though I began reading Attack on Titan in 2017, the whole enterprise felt like a lifetime and a well invested one.
Whatever Isayama-sensei plans to do, assuming that he chooses to continue in the manga industry, then I will be looking forward to his future works.
In fact, the very last page of the expanded ending may be visually interpreted as in Isayama-sensei extending an invitation to the reader to venture inside the Isayamaverse, an unofficial term I coined myself, into another world full possibilities and whether hope or hell awaits at the end only those looking forward to will ever find out just like Eren did.