It adheres to traditional Unix and new defined standards.

It's open source with a BSD License, which is much more business friendly than GPL. It's the real ancestor of Mac, that is being used nowadays.

Under NetBSD csh is csh not tcsh; also vi is real vi not elvis, nvi or vim. It's ideal for purists.

It's the most portable OS in the world when considering what architectures it can run on. It runs on very wide range of hardware, from toaster to satellites. This of course does not mean it supports drivers for many consumer facing products making it a difficult solution to just boot up and use when compared to other OSs.

It prioritizes source code cleanliness over anything.