Every scene with Yamamoto fighting someone is awesome.

Most of the arrancar fights I found to be disappointing. Kenpachi's I-win card sounds awesome but it's pretty lame in retrospect. Cirucci's deal was all about Uryu waiting to strike. Yammy's was skipped. Harribels fight with Toshiro was broken up, paused, and interrupted by Aizen. Wonderweiss won most of his off screen and in the only reason to watch the anime, the animated fight scenes, was dumped in favor of expanding on Coyote Stark's loneliness.

Aizen vs Urahara, Isshin and Yoruichi looked so good because in the ultimate showdown, they were the only ultimate showdown.