Meh endings are a very common problem with the genre, not exclusive to AoT. It's very hard to find a good Shonen ending that managed to please everyone. : r/ShingekiNoKyojin

Philosophy – aevumus ♤

Translations & Betrayals

Why Do SO Many Animes Have BAD Endings?

Shingeki no Kyojin (Attack on Titan) - generic discussion thread

MangaReview: (AoT) The Mediocre Ending for a Monumental Epic.

Nasuverse Discussion Post – Dragon Quill

AoT: The Obvious Reason Why The Ending Failed, by Lily

Spoliers ch.139] The Translation Error

Print Page - The Official Anime Reviews Thread.

What are the animes similar to Attack on Titan and Death Note? - Quora