The menu items were not grouped logically, eg in order to change something in one feature I had to browse through every single config page in order to find the related options. It was possible to do, and PFSense Support was phenomenal (by chance the co-founder answered the phone when we called Support), but the UI left much to be desired.
Compared to my experiences with the Sophos UTM, it's downright painful. With the UTM the UI elements of every part of a service are grouped together, and are duplicated in sections where it's intuitive to do so. Eg Certificate Management can be found in multiple places in the UTM but all things related to the web filter are in one place, all things related to routing are in one place, et al.