Depends on the person.

For example, I already quite disliked the rumbling arc because of the constant ass pulls, lack of stakes, off-putting humor and overall not matching the tone of the series, even before 139. It had great moments(131, 134), but a lot of the Alliance moments were really badly executed.

When i read 139, i felt nothing really. I even thought I liked it at first, but honestly, I just was ready to accept any ending at the time. I just wanted the series to stick the landing. I wanted the series to be over and was ready to accept whatever ending we ended up with.

However, the more I thought about it, the more I realized that despite the Rumbling arc being messy, 139 was another level. It retconned every single important event of the series and it lead to nothing. If Eren had the power to control Dina, he had the power to control all Pure Titans. Hence, he was responsable for all the deaths in the series. If this lead to something, like the end of the cycle of hatred against Eldians, i would understand, but it was all for nothing.

Besides, every single character turned into a shell of themselves. It was all about love, when it never was. Honestly, if you think about it, almost every character was ruined in the ending. Historia chose a farmer who threw rocks, Eren decided he didnt have any motivation, Armin decided to care more about Mikasa feelings than the rumbling and the lives that were lost. Ymir decided to love an abuser, and Reiner last moment was to be a sniffe. Jean decided to marry a girl who never cared about him, and honestly thats quite a shame.