[roywiggins]

There's no obvious minimal subset of features. Here's a feature Google Photos doesn't have: you cannot automatically sort photos in an album based on the filename. Either you sort by hand, or you sort based on the EXIF data. Picasa could, but Google Photos never got that particular tiny feature.

It means if you organize photos with a program, export them so they sort correctly based on filename, you'll lose your sort as soon as Google Photos gets its ugly hands on them. Google doesn't understand that EXIF times can be wrong.