Thanks for the patch, but this seems largely targetted toward images in a way that I don't feel comfortable with. Any sort of file can be uploaded and extensions can provide review UIs for various types of files.
What I'd like to see is a more general approach to this that can work with all file attachments of all types, including those without review UIs. I'd also want to see more of a thumbnail view, as changes with many files are hard to paginate through one-at-a-time.
I don't know that I have a perfect UI in mind, but my first stab is a scrollable row of thumbnails at the top that works like the review request page's thumbnails. Maybe allow it to be collapsed (maybe even collapse by default) in order to save space for reviewing purposes (particularly handly for large images and for PDFs when using Power Pack). That would go above the review box.
(It's important that if the box is collapsable that we provide some mechanism for review UIs to update their sizes/positions of elements when that collapse state changes.)