I don't run it right now (and won't anytime soon) as a desktop. Once I switched to using laptops exclusively, the driver story became too bad to work comfortably. But, I used FreeBSD on a desktop for 5 years, from 2005 to 2010.
I really enjoyed using it. The reasons for that are what others already mentioned: simplicity, well-thought-out organization of the system vs. userland vs. 3rd party packages (man hier), excellent documentation always available locally, ports, jails, pf, etc. It was all nice, but the killer feature, for me, was stability. The system simply refused to die, no matter what I threw at it or how I misconfigured it. At the time, Linux was a lot less stable than it is today - it could hang forever, corrupt the filesystem, or restart in the middle of doing something. Especially with proprietary, binary blobs and apps, rare as they were, Linux had a hard time accumulating uptime. On the other hand, FreeBSD worked, always. Well, it had no other choice, given that ACPI wasn't fully implemented and it couldn't suspend/sleep - it was a desktop but also a server for some private stuff, so that was ok.
Linux got much better over the years, both in kernel and userland. I have been using Fedora for close to 15 years now, and it works. I won't be going back to FreeBSD on the desktop, unfortunately. However, I'm tempted to try it again on an older laptop that plays the role of a NAS: no GUI, always connected to the router with a cable, always connected to power. I have Fedora running there, but I already use ZFS - it's great - so the switch shouldn't be hard.