Here's the summarised changelog for the new version, v16.1003.10012.0:
- New option to choose either a light theme, a dark theme or just follow your system theme choice
- Font changes in album titles, no more WP7-ish bold fonts
- Photos are now animated back to thumbnail size after viewing, mirroring the 'expanding' animation when originally selected
- Better album layout and smaller thumbnail sizing (three across on the editorial Lumia 950 and 950 XL)
Note the new theme selection (oddly called 'mode'!), plus the new, cleaner album titling and layout...
You can update Photos in the Store in the usual way if you're on the 'Fast' Insiders ring.