yepyep.
Its biggest problem is that it's very barebones and heavily lua-based. A lot of basic features you expect from a game engine are missing and require you to program them yourself. Following that is the fact that the BSP construction tools are total crap, worse than UE (meaning unless you're a modeler, good luck). The UI is also incredibly clunky, finicky to use, and extremely cluttered, esp. with duplicate options. It looks like a lovely Hammer-inspired work environment, but trust me, Hammer is more user-friendly.
Most of the hours I spent with it was trying to get used to it in hopes I didn't waste $100. The only things I really digged were the material importing an WYSIWYG viewport, both of which I only liked because my experience was limited to Hammer at the time. That shit's standard these days. I wasn't a modeler at the time so I have no idea what that process is like.
Overall, if you're a programmer and want to release a commercial game without paying royalties at all, it might be worth looking into. The dirt-cheap royalty-free license is really the only enticing thing about the engine. Otherwise, just use Hammer or Unreal like the rest of us.