Anyone ever use the Doom 3 BFG engine? Thread

Nobody talks about the Doom3 BFG engine, but it seems to be fairly modular and advanced. I'm thinking of working with it, but I can't find many people who have ever used it. In terms of free engines out there for FPS development, it seems to have some strong advantages:

- Completely open source (GPL)
- Unified lighting
- Works on Windows/Linux, and maybe OSX/Mavericks
- Multi-threaded like idTech5
- Tools for map creation included (in GPL Doom 3)

I'm also guessing that it has some important disadvantages:
- Smaller community of users/developers
- Might not work with large open areas
- Not much documentation

Any thoughts on the engine? I'd be interested to hear what people think from the developer, designer and artists perspectives...