Seemless installation. The ability to upload and incorporate Gedcom files. You can selectively plot genealogy data on a static or interactive map. It will connect to Google geoplotting for all my entries and get the lat/long of their locations. I could add much more but the best thing is that it's built in a way that is very flexible for your particular needs.
The only element I had any difficulty with was to add a button to "create article" allowing my users to add a map to their own submissions. This may have been my own fault as I have many other extensions integrated into these article submissions and not all of those work as well as Joaktree.