Full Metal is by far your best map to date, and as always with your maps, it's exceptionally well put together. However, the map is not without its flaws.
While the aesthetics are very clean and believable, they're nothing particularly refreshing. This is Halo 5, and every other map out there (and the majority of dev maps) are UNSC aesthetic. It's over done and and incredibly stale at this point.
Pathing for the most part is pretty solid. There are a few nitpicks about it, mostly relating to the upper level on rocket side. The lift leading up there isn't readily apparent (I didn't notice it myself for the longest time), and neither is the actual path that leads directly up to the level either.
Those nitpicks aside, it's a pretty solid map. I wouldn't go so far as to call it great, but it's one I do enjoy playing and wouldn't mind it coming up regularly in custom lobbies. Solid 7/10. Well done.