NetBSD is my daily driver. Excellent piece of software. I was a GNU/Linux user since forever and I switched to NetBSD few years ago without looking back.
There is a helpful community, solid development method, strong technical community, conservative model, focus on correctness (thousands of ATF unit tests) and usefulness. There are commercial vendors around this system and the portable package collection (pkgsrc).
This system is improving rapidly and catching up after competitors, not necessarily being the first it usually produces better solutions.
NetBSD isn't an OS that will hold your hand during installation and set-up, but it's great for server applications and pretty good for desktop use. It also has a great source-based package manager, pkgsrc.
Tried NetBSD 7.1, but couldn't get Networking to work even though I tried to follow the directions. I do give credit for NetBSD's success with embedded devices and that it can run on a huge number of platforms. The main flaw is its very difficult to get it to work properly on the desktop, much more so than Slackware. With the exception of GNU/Hurd and Minix, NetBSD is the oldest FOSS operating system still maintained. A GhostBSD style variant of NetBSD would be welcome!