Very enjoyable level, and I'm glad to see all the "big ticket" issues I pointed out fixed from the beta version.
From what I understand, the term "Metroidvania" is an ad-hoc name for a subgenre of (typically 2D) adventure platformer where you explore a large area that gradually opens up more and more as you obtain new abilities or otherwise unlock new zones, and also typically involves a lot of backtracking through old areas. As the name implies, this style was pioneered by games like Metroid and Castlevania (specifically Symphony of the Night). Technically, the original Nifflas levels The Machine and A Strange Dream are also Metroidvania levels. By contrast, Knytt Underground isn't so much a Metroidvania because as soon as you hit the main "open world", you already have your full kit and can go basically anywhere.
Anyhow, before I digress further, I'll say again that this is a well-done level, and the challenge for the most part isn't too distracting from traversing the various areas. The music choices are very nice. I particularly like the use of SineRider's tracks from the Music for Sleeping - Volume 1 album. I also appreciate the reference to Last of the salad days (however unintentional it may have been).