The change to inserting shortcode (the square brackets you're referring to) instead of a direct HTML was made intentionally to allow for inevitable changes by Google to the way Picasaweb (which is being migrated to Google+) references photos.
The shortcode is processed by the plugin and can, if necessary, update the HTML it generates if required by Google's impending migration. Thus, if Google updates something that breaks the photo links, a simple update to the plugin will allow all previous posts with photo links to continue working.
With that in mind, if there is a strong need to continue creating the HTML directly from the image selection dialog, it might be possible to add an option to toggle between those two methods. But any posts created with the static HTML would break when Google eventually completes the migration, so I tend to think adding this feature isn't necessarily a good idea.
I would appreciate anyone else's thoughts on this issue as we try to decide the direction of the plugin.