In terms of character stuff, the pre-SS volumes are great and very original (which reminds me, Kekkaishi is a great manga that's more like those early volumes). SS was more plot-driven, but still has some great moments, we were in Rukia's head more, Mayuri's fight was important to Uryu, both the Soi Fon fights and the Byakuya/Renji fights clearly had a ton of emotional meaning to each fighter.. they mattered.
Of all the Espada/hueco mundo fights, only Aaronneiro has any great character moments with an existing non-Ichigo character. Also the plot barely moved, it was a giant SS-sized arc where most of the action was eliminating characters who we first got to know during their fights, there was little personal connection. Uryu, Chad, even Ichigo didn't really develop as characters during it. In the end, a bunch of characters, some interesting, some not, were introduced then killed almost to the last.