this is quite an old topic, but i'm kicking it nevertheless because i'm using CPG1.3 now and have used/is using gallery too.
I didn't participate on this discussion until now because I wanted to see how the upload-pics-features of CPG1.3 looks like.
If it comes to flexibility and ease of use, coppermine is better. The usage of a database makes this possible. Adding albums and changing descriptions is a breeze. And the looks and feel of coppermine is very flexible too.
Nevertheless, gallery is much better when it comes to organizing and uploading.
In terms of uploading, they have 3 major modes: the most important one, their integrated java-program to upload a batch of pictures from one's computer is very efficient. The second one is a form-based multiple filesuploadmethod, much alike coppermine's. The third one, and my favorite one,is their URL-based upload. Instead of adding the URL of 1 image, you can add the URL of a directory or webpage and a list of all possible uploadcanditates will be shown. Select the images you want and it'll be added to your gallery.
Another good thing of gallery is the way they organize files. Instead of one huge directory and depending on a database to link to the right file, the images are indeed inside folders and when deleted or moved, they physical location will change too. This maintains a very clean directory structure. And it's less mysql-connections of course (gallery use only php)
And finally, the permissionssettings of gallery is much better than coppermine. It's easy to appoint "moderators" to help out with the organizing.
But... i'm using coppermine anyway. mayinly because of the looks, but also because I can use mysql to edit descriptions a lot of images at once. However, it'd be recommendable for the developpers of coppermine to take a look at the competition and learn something from it.