I´ve been administering ISA firewall for a while and a really like it a lot! Always recommend it, because of it´s great features and the excellent cost-benefit compared to others firewall on the market today.
To list a few of ISA firewall features I can say it has the Web proxy/caching server, VPN (Remote client access and VPN gateway), application layer inspection, pre-authentication and comprehensive real-time monitoring logging.
Despite, the logging functionallity is really good on ISA. Some firewalls does not come with that (you have to pay for it). Many ISA administrators, when troubleshooting don´t check a very important field IMHO (in my humble opinion). The Result Code field provides really important information when troubleshooting and can help you to identify what is going on the firewall.
Some of the errors are not very understandable and some can give you a clue of what the problem is. For those cases where you can´t understand, you can check the meaning on MSDN web site. Error Codes.
This blog entry was inspired by questions asked on www.isaserver.org message boards, which many of them can be answered by checking Result Code field.