I think it's misunderstood that the ending is the issue when it's really_the execution_ that failed.

At the end of the day whatever the ending was going to be some people will hate it and others will nitpick the logic plot holes. However everyone got to where they were supposed to be in the story.

It was the terrible time jumps and sudden twists and deaths and poorly displaying it on screen that made the last season really disappointing.

Also the series had the unfortunate fate of peaking in season 4. Compared with Breaking Bad which had its best episode in the last season.