Some people expected and wanted some big, action packed ending with a lot of tension going on, but that would've been one of the most contrived endings possible. Just because the series had intense moments doesn't mean that the finale should be crammed to the rim with it. The finale should serve its purpose: tie up all loose ends and make it interesting, which it did in my opinion.
Story and structure wise, Ozymandias was the climax and this was the resolution. Shit had hit the fan, and everything had crumbled around Walt leaving the final pieces of the puzzle to be put in.
I think finales are inherently set up to disappoint; they're the absolute final taste in your mouth. There's almost some sort of unspoken expectation for a finale to be better than the entire series that came before it, which is impossible to do.
Very seldom is a series finale good and satisfying. The number of series finales people would deem "good and satisfying" can be counted on one hand. To my knowledge, everyone hated the ending to Lost, the ending to Dexter was mixed (but mostly negative), the Sopranos was extremely polarizing, etc. Very few are unanimously considered good by fans.
I really do think they ended the series as good as they could've and pleased almost everyone. I don't know if there is such a thing as a perfect ending to a show, or what one would even look like for Breaking Bad. I think if some fans got the ending they wanted, seeing it executed still wouldn't be satisfying to them.
Let me be clear, too: I'm not saying people who didn't enjoy the finale are wrong by any means, I'm simply saying the ending we got was the best one we probably could've gotten.
That's just my two cents. A great ending to a great series in my opinion.
