Regarding my first impressions above:
I was (also) wrong about the "having to swipe to key pad" part. I've edited the post accordingly. If I find a thumb position where the finger print works all the time, it'd be pretty usable, even with having to press the button.

Regarding the Gallery:
While the multiple ways to exit an Image view are a bit irritating at first and it's not the most beautiful thing I've ever seen, I agree it's really much, much better than the abhorrent tap-to-split view and a lot less confusing for new users.