I had stopped reading bleach when Toshiro went zombie and after the final chapter came out, I binge read the final war arc from the start . After reading the last chapter my reaction was pretty much same as everyone who had been reading bleach for a long time ; " What the hell ?! " In any case, all this dragging of final arc; that build up, went down the drain!
All that sudden power-ups that came out of no-where and repetitive fights aside, In my opinion Bleach's downfall at the end can be attributed to a lot of things but these 2 things comes to mind:
1) Either Kubo made Aizen way too good or cool a Villain,
Or
2) He seriously chose the wrong guy (Ywach) to be the Final Boss!!!
Edit:
P.S : The women in bleach are one of the sexiest i have ever seen in anime/manga. (So I guess that's a plus point)