Small, light on resources, very fast, flexible, comprehensive format support, good user interface, no bugs that I've seen. It doesn't get any better. I've uninstalled PeaZip and 7-zip, although they are each good programs (7-zip, regrettably, has become a poster-boy for inward-focused development).
The interface could be improved to excellent by: 1. Offering a portable version; 2. Making the settings options less cryptic or providing explanations for the options; 3. Better choices of context menu options; and 4. More extensive toolbar.
A changelog would be nice, as well as more communication from the developer on his forum.
License: Free Details...