UI3 is very close to being acceptable, with the sidebars being pinned to the edges once more. However, the placement of the toolbar at the bottom is distracting. I actually never use any of those buttons, preferring keyboard shortcuts, and would be fine if there was an option to just hide it permanently. Or, like in photoshop, turn it vertical, and pin it to one of the sidebars sticking out a bit that would also be ok.
I’m sure you’re getting hundreds of messages like this, just tossing my feedback onto the pile.