Honestly, having read the whole thing in Japanese, people are over exaggerating how bad the ending is. To me it feels like most people who keep parroting this sentiment over and over listened to a few opinions and never bothered to read it themselves. To be completely clear, the ending is not good. It was a pretty big disappointment considering the quality of volumes 1-9, but the series as a whole is miles above some of the trash that gets consistent praise.
To those who are anticipating the worst, I'm hopeful that by the end you can say to yourself,"it wasn't that bad".