I’ve never really used Genesis, so I can’t speak too much on what’s different.
The initial look of each theme is quite similar. I think the difference comes from the fact that using the Customizer you can turn GP into anything you want that will be unique to your website.
With Genesis, you can choose a child theme which hundreds (maybe thousands) of other websites are running at the same time.
I also like to think that GP is considerably easier to use, while still allowing devs to hook into the code using hooks and filters to build really advanced sites.
I really try to make GP beginner and advanced user friendly.