The feature set is fine and is rarely a problem.
Cisco makes horrible UIs, so the interface is something that should be improved. Usability is poor and it doesn't matter how good the feature set is. If the UI, whether the command-line interface or GUI, isn't good or isn't usable, then you're going to miss things. You may configure it wrong and you're going to have security issues.
Security vendors have this weird approach where they like to make their UIs a test of manhood, and frankly, that's a waste of my time.
The SNMP implementation is incredibly painful to use.
I have been using Cisco Firepower NGFW Firewall within the past year.
I work with a lot of different IT products including three different firewall solutions in the past 12 months.
Everything has room for improvement.
I would rate this solution a five out of ten.