It's not that it's a bad forge mode, it's the best in the series. It's just that, for me at least, the content updates make building a map at the moment pointless.
I will build a map, content update comes out with features and objects I wanted for that map, I will need to return to that map and spend time editing it or rebuilding it just to put in the new features.
I just don't bother with halo 5's forge because I Know a new update will come out and it will make my old maps pointless and redundant unless updated.
A good example of this is the scenery textures, If I built a map before the textures came out i will need to revisit it and select every bit of scenery and adjust it's texture.
I'll probably go back to forge once the content updates stop coming.