For a server - it's fantastic if you're a reasonable adult and if you don't have a compulsive need to install every shiny new "app" you find on the internet. Terrible if you hate reading any kind of documentation. Terrible if you already decided that some of its core concepts are stupid and try to force stuff in order to mimic your favorite Linux dist.
Takes some knowledge and planning to set everything up properly but when it works, it works forever.
ZFS works as intended. I hear that it's miles better these days though in Linux.
Jails will make your life so much easier.
If the software isn't available in the ports tree you don't need it. You may want it but you really don't need it (bro just download my Docker image, I wrote a webserver in rust bro I promise it's super stable and it's never been done before bro). Enable Linux binary compatibility or fire up a virtual machine with a tiny dist if you're a masochist.
I personally like the default firewall, pf. It's got a bad reputation in some circles though.
No systemd.
No systemd.
No systemd.
I guess it depends on the use case. If you prioritize network and zfs performance, sure. There's a reason why the Netflix CDN or your router runs some BSD derivate.
I'd argue that the jails are a feature that hasn't been replicated. Each jail is a container and can be set up as an isolated environment with its own filesystem, network stack, set of user accounts etc. I know there are a few similar solutions on linux but nothing that is so deeply integrated.
Yes, of course. I believe it was a NetBSD developer who initially wrote it.