The only "catch" is that there's not a lot of content present at the moment. Textures are limited to "office" themed textures, the same is for map models, there's no implemented physics system, and there are only two weapons and they're both instant kill. Making new content like textures and static models is moderately easy but adding new weapons would require a knowledge of C++ and a good grasp of the source code (which is available.) there's an offshoot with lua scripting but it's really immature.
