Previously when you did an image search, you'd see multiple pages of thumbnails with text showing the file name, dimensions, and a description associated with the image. Now you'll only see a mosaic of tightly packed image results with larger thumbnails and no text. Hovering over an image result will blow up the image, reveal the hidden metadata (for some images), and show a link to search for similar images.
Although you're viewing far more images on one page, it's actually easier and faster to look through them all because of Google's "Instant scrolling" function. Scrolling through a full set of results didn't stall or slow down my pages as the images loaded. You'll still see small page numbers to the left of the results interface to help you keep track of where you are. Google's also transitioning to image ads rather than strictly text ads. You'll find them at the top of the page.
When you click on an image result, instead of viewing the originating Web page with a frame at the top, you'll see a blown up image in the forefront of the screen with the Web page dimmed in the background. To the right of the page you'll see the URL of the Web page and a link to the full-sized image. In addition to the images dimensions next to the link for the full-sized image is text telling you how much bigger the full-size image is than blown up image shown on the page.
Clicking the "X" on the blown up image will take you directly to the originating Web page. I like this layout better than the framed page used by the older Google images format, because you get a much better idea for the size of the image (plus, you may not want to click on the full-image link). It would also be nice if clicking the image would take you to the image's position on the originating page—neither the old or new versions of Google Image Search has this ability.
Google managed to display more and larger image results without slowing load times, and made it faster to find images for which you're searching. The redesign is being slowly rolled out to all users by the end of the week, and currently only works on PCs running Chrome, Safari, Firefox 3.0 (and up), and Internet Explorer 7 and 8. Overall, the new Google Image search is a much more efficient, aesthetically pleasing way to view image search results.