I think where obsd really shines is in the small infrastructure department, name servers, routers, time servers, web servers, mail servers. Obsd boxes tend to be easy to administrate, predicable and most importantly boring. It is a great system to build the back end of your small business or home network.
Personally I think it also makes for a very nice desktop system. But I like my desktops thin, a tiling window manager and lots of terminals. If you enjoy fat desktops, there may be a bit more friction. One reason I like it for desktop use more than other systems is that the software packaging feel higher quality. It is not a huge difference. mainly I have found obsd packages to more reliably work when installed. and those heroic obsd package maintainers tend to put a note in /usr/local/share/doc/pkg-readmes/ that will get you started.
It's extremely simple and straightforward for networking devices. Setting up an OpenBSD router or gateway is such a pleasant process.
The documentation in all aspects is superb, and you can run all sorts of servers just fine (ports is full of common software). You can technically use it as a desktop workstation too, but I can't point to anything that really stands out in this aspect — except perhaps the strong focus on security.
It’s my daily driver. Simple and it works.