Just from memory as I uninstalled it already:

* Settings in one place, that way I could have probably easily found out how to remove the annoying zoom-features.

* Batch conversion

* Slideshow: Add files/folders, not just a textfile or folder

* Slideshow: More options in general, e.g. random or unique random.

Thanks. I never use the slideshow features so I guess I didn't notice.

I do think it's odd to expect an image viewer to be able to do batch conversion, though. That's what I meant by a read-only image viewer.

It does support batch rename, though. And generally I want to resize images while looking at them, and not go elsewhere for that. But only when I want it to, no automation.