ZFS, Dtrace and much better containers on Linux
First time Linus published his stuff, I laughed: I worked at a research lab and had full UNIX souce code as well as a far superior micro-kernel OS (similar to L4) in my hands. I also had a 80486 running both pre-SCO Unixware and 386BSD (I had even run Microport Unix on a 80286). And I had SunOS running on a Sparcstation 1. Couldn't see me using Linux for years, especially after reading the task switch source code, which used the horrible Intel task state segments.
I guess for Linux the GPL made quite a difference some time later.
While I continued to evaluate all those BSD and Solaris variants for x86 during those decades, I finally gave up BSD and Solaris when everything I wanted had arrived at Linux: ZFS is as good as it will be outside Oracle on Linux, Dtrace I thankfully do not need and systemd to me is mostly something Solaris inspired.
The biggest difference, however is containers, more specifically OpenVZ containers. Those have been so much better, more mature, manageable and given a degree of flexible control, that VMs couldn't ever achieve, while I could still use or combine them with VMs if I wanted to. These days OpenVZ gives me a unified API and CLI to run containers, even nested ones with Docker as well as KVM VMs, while I can still run VirtualBox or VMware Workstation as type 2 hypervisors.
Have a look and dry your tears: https://openvz.org/Virtuozzo
Been running it for a decade with PCI-DSS compliance on hundreds of servers and never looked back to paying for an operating system.