Main negatives about BSDs: more fiddly, not necessarily as well performing as a stable well optimised Linux release (read RHEL/CentOS), some compatibility problems (usually due to crappy programming by Linux-heads), you might have to compile a load of stuff yourself.
The big wins are however: rock solid, wonderful documentation, entirely cohesive base system, small, big enterprise features (ZFS, mandatory access control, tracing frameworks, awesome network stack, security, ACL support and better hardware support.
When I say better hardware support, I mean the drivers all work rather better than their Linux counterparts rather than being plentiful and the supported platforms are plentiful and reliable.
I can drag a 17 year old SPARC64 machine out of the cupboard and just use it.