I finally downgraded my 2012 Nexus 7 today back to KitKat. It was essentially unusable running Lollipop
My experience on the Nexus 10 has been the opposite. KitKat was so bad that I had to go back to jellybean after a couple of days. Lollipop, on the other hand, has been smooth, light, and rock-solid; no issues at all. Best release for this device ever.