The rom hack is... fine.
The thing that dampers my experience the most is that there's a ton of empty space and some mazes that I just find myself long jumping around.
It really screwed with the pacing.
In short, the oversized levels are a problem.
The game itself is a little janky but that's totally overlookable. Examples include the awkward transition with the engine room door, Mario becomes Metal Mario for some reason.
The stages also have a lot, and I mean a LOT of places where you can look over geometry and see through walls in other parts of the stage. You should raise the walls a little and add some floors, so this happens less. It's hard to articulate what this problem... is? But it takes away the immersion a little.
Pretty good :)
