The URLs and file sizes provided valuable information at a glance that I now need to comb through methodically. Additionally, I find the design distracting and clunky. The mouse over highlighting works its magic when you are anywhere near a picture, not necessarily on top of a picture, which inadvertently draws attention away from scanning the other pictures.

What are the advantages of this design?

I agree – Google seem to have taken the Microsoft route of taking something that works well and messing around with it until it is broken and annoying. I think it’s dreadfully clunky now.
The information wasn’t in the way in the first place and, when searching using images, that information is very important as a guide – to what sort of site you will be going to, whether that site had more images related to your search, the name of the image (important clues as to search relevance) and what size image you could expect. All of that information could be assimilated at a glance for an entire page of images.
Now, you have to hunt and peck, like a drunken typist and searching by image has been rendered less efficient because of this.
If they wanted to “fix” Google Image Search then they should have worked on what was missing from the functionality, like the ability to dictate how many images are displayed per page, the size of thumbnails etc.
Bad Google, bad.