About time I quickly review this in a rush.
In terms of the graphical aesthetics, it may look rather pleasing to a typical player overall.
Already in the starting level, there's the brightness indicated from the colour choices. (Kind of similar to this one GFX-only hack I know, but it didn't bother me.)
I particularly liked the underwater section where you decorated part of the level with red eyes, as well as this section:
While the level ideas do appear to be potentially fresh, at the same time I found the executing of the level design standards rather poorly to my tastes, somewhat underdeveloped.
Here are some rather picky examples:
In this section, this is a rather clumsy way to place coins next to a question block due to its heavy unsymmetrical placement.
This part: Any experienced SMB player will instantly recognise it's a barely designed 2-4. Keep in mind you wouldn't want the levels to be too similar to the original SMB.
Even if you do want to keep some artefacts behind, like 1-2 of the hack, at least make sure the transitioning between your own style of levels and the original assets smooth and not just a sudden appearance of them.
Not to mention, some levels needed the "breathing space" and filling in gaps such as more enemies to make it feel less "empty"! While I may not be the Bob Ross of level design either, eventual improvement and/or looking at it a second or third might as well help you to get up to those standards everyone wanted. Take a look at SMB2J/SMB Special's levels. How do they make certain assets of the level still relevant?
Just for another tip: Reason for the "1-<pipe tile>" glitch is because of the default staircase's value: It must stay at zero, no other value.