Gameplay is addictive and extremely fun. It feels like this perfect combination of Rat Game, and more "true" roguelikes like The Binding of Isaac: it's satisfying to go through and you can get pretty far on most runs if you try.
Even the way the items themselves are presented feels fresh and new: I'm getting tired of the old 32x32 graphic slapped on a stone slab, and the little paper bits was refreshing to see, and the lower quantity of items and certain upgrades help to keep players attached to their weapons for much longer than in something like Gungeon.
The Newgrounds crossover weaponry was handled fairly appropriately in my opinion: it never really draws too much attention to itself (except for maybe the Isaac and Piconjo ones), which is alway nice with stuff like that.
Unfortunately, a lot of my criticisms lays with the art direction: deviating from Krinkles' stuff is always cool, but there's still some boundaries with the source material I feel were pushed a bit too far here: the art direction of Madness is defined by the over-the-top badassery of late 90's and early 2000's action flicks, which is very different to how this game presents itself.
Seeing as how this game tends to base its aesthetic off something that contrasts the original art direction of Madness significantly: cutesy Japanese-style streetwear, things end up being somewhat hit-or-miss for me in terms of character design and artwork.
If this was built as an original game, and there was a bit more content to play through, I could definitely see myself paying for a retail version on Steam or itch.io.