There's a lit of piece of polish I look for in maps, and I consider it quite important. And that is bullet ricochets on doors. Here we have a generic door in Hammer: Let's have a look in-game: Notice something wrong? We're firing a minigun at a metal door, and it might as well not even exist! Good thing there's an easy way to fix this... You'll notice that I've done two things: first, I textured the func_door with metal/ibeam001b. "But Nineaxis", you say, "now that door is going to show up in game! I textured it with nodraw so it wouldn't!". And that's why you go into the properties of the func_door, and change Render Mode to Don't Render. This, as the name implies, means that the func_door will not render. But the surface type is still there, and the metal texture makes it metal. Let's take another look at this door in-game. That's better.