So, a beta version of the new garrysmod is out.
Straight from garry's keyboard:
* It's on the EP2 base.
* DX7 users will still be able to run it, but will probably get graphical problems with some of the new shaders, like the particles. If you're still running DX7 I'd recommend looking to upgrade ASAP. You won't regret it.
* Owners of EP2 will get new NPCs.
* Owners of EP2, Portal or TF2 will get new content from those games.
* Lamps cast real shadows (on hardware that supports it)
* Spawnmenu has been totally re-designed from scratch (and completely in Lua)
To run the beta you need Garrysmod 10, Orange box, and an account on garrys forums.
Here are the instructions and official download page. http://forums.facepunchstudios.com/showthread.php?t=441466
(you need to register to see the page.)