GUI is pretty simple and easy to use. Good intrusion detection. Allows File sharing and Network Neighborhood visibility to be easily disabled. Informs immediately of an attack, and notes the attacker's host name and IP address. A corporate version can centralise configuration, policy and alerting.
Documentation is pretty good.
It would be nice if power users could customise the rules more. It would be better to be able specify port ranges or wildcards and even better to be able to filter state based protocols like ftp. The default configuration does not protect against Trojans like Back Orifice. BlackICE waits until a connection is made before it takes action, it doesn't prevent a connection by shutting down the system's ports. Outgoing ports cannot be blocked.