Ghaleon and Letters are both right - there's a big gaping hole in Halo 4's Forge offerings. There's no big, open, empty, flat area for Forging.
Forge has become a tool to build maps, from the ground up. But the actual spaces in Forge don't allow you to do that. Just look about the videos. You'll see all kinds of intricately designed hills, rocks and cliffs and structures and terrain. It looks nice and it' very well design and crafted. Kudos to the artists and level designers. But it's shite to Forge on. Say you want to play two bases opposite each other. You find a big enough spot, but oh, wait, there's a river running down the centre, and an outcropping of rock that you can't delete. And the terrain near one of the base locations had a definite slope to it. and half a hill that will force you to either raise your base building heigh to compensate or force you to sink pieces in the ground.
The actual Forge spaces aren't letting you express yourself. Forgers want a blank canvas and a nice set of tools and they are happy. Instead they are given a used canvas, a beautiful canvas sure, but one that already has a pretty well defined picture on it already. So you can only work on top of the existing work present on the canvas and no, you can't change anything on the canvas or alter it in any way. Just work on top of it.
343 and Certain Affinity may understand what 90% of Forge users want and with Halo 4 they are giving it to them. But that 10% are the hardcore guys. They don't want a helping hand. They don't need a template, and they aren't happy to paint by numbers. They want a blank canvas.