Put simply, it's more integrated and unified than most Linux distributions. Instead of packaging this thing from here, that thing from over there, and ramming

Put simply, it's more integrated and unified than most Linux distributions. Instead of packaging this thing from here, that thing from over there, and ramming in this new toy from that place there, everything in each release - tools, userland, ports, kernel - moves in lockstep. The result is an OS that's very consistent once you figure out how it does things, and rock solid stable. It takes a bit more tweaking to get, say, your compositing window manager running - but once you do, you can be guaranteed it will keep running - even when you change or upgrade other things - with all the stupid consistency of a rotating planet unless you screw up and do something very bad. Also, in my experience, it's much more customizable than Linux. The kernel sources are included in the distribution, right there for the building, and the process of configuring and making your own kernel is fairly straightforward, even easy. Contrast with the closest thing I've seen on Linux, Gentoo - which is significantly more involved. That may seem like an obscure point, but if someone walked up to me and told me I needed to put a *nix on a server tomorrow and strip it down to get every last iota of performance out of that server, FreeBSD would be the first thing I reached for.