As pointed out by the Huffington Post:
The new design moves caption, comments and advertisements to the right-hand side of the picture. Previously, users could view captions and post comments directly below the photo.
I thought the new design puts emphasis on the photo more and makes for a better experience, since mostly commenting is secondary to actually viewing the photo (hence the left to right flow). Of course, the biggest jarring feature aside from the photo is the advertisement, but I quickly turned on my blinders towards it.