I've seen a few comments like this in response to my posts, so some elaboration and (hopefully) clarity is probably in order.
Generally speaking, I only build BTB maps, because that’s what I like to play. I built a total of five maps in Halo 3, maps that were polished and iterated on many times to a point where I was satisfied with them. (I'd started over a dozen, but only five made the cut, so to speak.)
I built just two maps to completion with Reach, despite the expanded tool set and dramatic increase in ease of use. As with Halo 3, I started over a dozen. I only built two to completion in Reach because while I kept coming up with map ideas, for the most part they didn't fit in with the geometry of Forge World. And to build them up in the air – as I did with one of the maps – placed serious creative limitations on the map: it meant every surface had to be flat and grey. And then in the end, the use of nothing but Forge objects as the geometry cratered the frame rate, making them unplayable in BTB HaloGAF customs, which is why I built them. Both maps were killed that way. I spent weeks working on them and one playtest killed’em dead.
One of the maps I attempted but never completed was set in the Gulch. But the terrain was uneven, and the space asymmetric, and so I kept having to change my designs to fit the geometry. And after a week of trying to get my ideas to fit in there, my original ideas were unrecognizable and I gave up in frustration.
What I wanted in Halo 4 was this: A big open flat space like the basin on Sandbox, but an open grassy meadow instead. And then 5-6 different grass-textured large objects to place to form my own hills on that space. Then I could dream up a map - symmetric or asymmetric - and make it as flat or hilly as I wanted, without the result looking like a grey metal dungeon. Toss in a range of rocks, tree objects, and the suite of additional Forge objects, and you’d be able to “accidentally” make beautiful maps, as the developer on the video said.
Right now it looks like the three Forge maps have the same set of limitations as Forge World: no big open spaces to build on. So if I dream up a BTB map, and that map does not fit in with the highly detailed geometry the map designers came up with, I have to use all Forge pieces. And then those pieces mean everything is flat and grey, which everyone hates because it's boring and ugly. And even if I manage to make a map I like, despite it being flat and grey, I run the risk of cratering the frame rate and so end up with junk in the end. (Again, this is how my work in Reach all ended.)
That's why I'm bummed out about Halo 4's Forge.