I run a Stars Without Number game and I love it.

My favorite thing is that they are all inter-compatible. SWN/WWN/CWN are all essentially the same system and can be used interchangeably.

Sure, as @tissek mentioned, the system is pretty simple and the options for martial characters are a bit lackluster compared to other games, but that doesn't stop us GM's from homebrewing things. In fact, I think that's where Sine Nomine RPG's really shine, the ability to homebrew much of what you need and ready made resources to do it.