Forge is not seen as an industry standard level editor and in my opinion its not worth your wile learning the in’s and outs of it if you what to get some core level design and game engine skills. But I spent over an hour tonight with my bother just playing around in Forge on last resort just making our own simple map. It was far from close to any solid kind of level design like I do in Unreal but it was great fun flying around the map finding different ways to block of doors, and then testing it to see if you could get through. I think for someone like him who has never really been into game design much, its a nice little package, and for a select few may lead on to bigger and better things.
I have to say some of the stuff in Forge has really impressed me as well, the D-Day landings re-created and stuff like that, which is actually sold to play. Forge may not be able to import static mesh’s or alter terrain, but in my opinion its a very worth wile part of Halo 3.