I definitely lost interest around the Arrancar arc. For me, Soul Society was the peak of Bleach, and once it was over, the series never got back up there again. Too many characters being introduced rather than really developing the ones that existed who were still hanging around (Tatsuki deserved better, and her whole position as Ichigo's oldest friend and the stuff about her gradually developing powers was so interesting it was just wasted and she had such a cool design aaaaaggh), and Ichigo's lack of a strong personal motivation or long-term goal really started to harm the series.
It's sadly a victim of a common problem; the series got so incredibly popular that the editors got scared to touch it. Tight's wild ideas were part of what made the series great, so I get it.... but he really could have used more guidance on story structure and stuff.