I liked both of pLaw's previous maps, but this makes them look decidedly amateur (and they are, of course, not).
I'm generally not much of a Metroidvania person myself, but the weapon gating works quite well here, tying in well with the overall level design—which is where pLaw knocked it out of the park.
Great big picture architecture and small-scale details, with excellent level flow and suitably nasty, well-conceptualised fights on Nightmare (but, crucially, never unfairly nasty). The last arena is a standout fight, one of the better ones I've played recently.