I rank CS5.5 higher than CS6 for a few reasons. First, Cannon XF and Sony Xdcam codecs were broken when the software was released. Constant glitching during playback. Both of these codecs worked in CS5.X. There was a long wait for a crucial patch for this in the form of the 6.02 update. This was the first time in ten+ years that Adobe left me hanging with broken software for so long.
It is my understanding that many users are still having issues with AVCHD material that function fine in CS5.X
2nd, I didn't appreciate the GUI changes. I, like many others used the Jog and Shuttle interfaces often. While other controls were optional for the source and program monitors, someone one the design team laid down the edict that there shouldn't be transport controls. This sort of falls into an overall pattern of gui and keystroke command changes that I felt were not enhancements, just different, or worse.. neutering. For example, I recently posted about my displeasure with the changes to the three way color corrector. CS5.x I was able target and affect the Video input/output levels of Highlights, Shadows, Midtones separately. So if I wanted to stretch the blacks without affecting midtones or highlights, no problem. From what I can tell thus far, CS6's 3-way CC has only master Video input/output level adjustment. Less useful = neutered.
I won't say that there hasn't been any utility added. However I think a lot of the design thrust was geared to appease or attract users from other NLEs (read Mac/FCP). PC users ended up with a product less functional than CS5.X.