What do you like best?
The best things of this product is how modular it can be and the community support it offers.
pfsense has a range of modules/plugins that can be added in order to shape pfsense to your needs, there is a wide selection and you are sure to find something to do the job. If for any reason you are unable to find a module to do what needs to be done, more than likely a question has been asked on the subject and an answer is easily found, if not you can pose a question on the forums and you will be met with a very patient community.
One of the main benefits is the capability for multiple WANs, allowing you to route traffic how you see fit or even load balance.
You can add squid guard and block/allow websites on a whitelist/blacklist.
Aliasing allows you to add multiple IP's/networks/hosts under a single alias and make firewall rules based on this, so rather than creating 250 firewall rules for 250 nodes, simply alias all 250 and make a single rule for that alias.
There are pages devoted to graphs so you can monitor your network traffic, your physical NICs and the server itself.
There are a ton of features and all the basic/advanced networking needs are met.
What do you dislike?
There is very little I have found I do not like about pfsense, although I have not tested every single possible feature, my experience has certainly been very positive. There are two things however that do spring to mind.
I was unable to achieve port forwarding for a VPN. The VPN was PPTP (admittedly I never tried any other methods) on a Windows server. Despite countless hours searching and reading the results and numerous attempts of changing settings, I was unable to use the VPN (had worked previously with a paid firewall solution), whether this issue still stands or was entirely my fault still remains unsolved.
After approximately three years I have found pfsense to become slightly flaky. I have only experienced this with one box (the longest running). Whether this issue boils down to the physical server and/or components or whether this is due to changes over the course of time/corruption of configuration files, is again undetermined.
In reality I have not experienced any real downsides of the solution I cannot link back to me.
Recommendations to others considering the product
It's got a great fully fledged gui and it's linux for shell users. Install it, try it, any problems the docs or community will come through.
What business problems are you solving with the product? What benefits have you realized?
The product has personally helped to act as a firewall protecting and controlling both internal and external traffic on the network.
It has allowed me multiple WAN connections. With aliasing I can quickly group servers, computers, security equipment etc. Using the aliasing I have been able to dedicate WAN connections for specific purposes ensuring the bandwidth is distributed as necessary with a single firewall rule.
Modules like bandwidthd help me check the hosts consuming the most traffic, squid to help me monitor traffic and squid guard to help me block or allow traffic, make this a great solution.
After moving from one paid licensed solution to another I have found pfsense to not only be free, but completely wipe the floor with anything paid for previously.
My experience with this product is extremely positive and I would definitely recommend it as a great solution.