It’s awful. I’m sorry to be blunt, and said with no offense to those who worked on it.
A lot of the recent improvements are great, but this is one of the worst changes to this platform in a long time. It is an uninspired change and there are so much better ways to display media.
The third and fourth pics in a given post are entirely lost on the timeline. Unless someone stops to swipe and see them, they are effectively lost.
Please look to Flickr’s pages for inspiration in having a dynamic and responsive way to display photos in various sizes.