Tip: You can use Lunar Magic's Overworld Layer 3 Editing system to edit or create your own layer 3 images (castle bricks, fish, rocks) and apply unique effects per level via the Layer 3 Bypass in the main editor.
Berkay, I know you're trying to provide helpful feedback to the author so they can improve, but I don't think that would accomplish anything since he has been inactive for five years and hasn't shown any sign of returning.
You must realize that a lot of these old hacks were made by people who gave up SMW hacking long ago.
Levels usually feel like each other because you keep to use the same enemies and ideas. SMW has plenty of nice sprites and tiles: use them. This tutorial may help you too.
Aesthetically, they could have been better too. It sometimes feels empty, some more decoration would be nice. Not a fan of the background in Sugar Hills 3 and 4, too, I don't understand why you put cut-off tiles. The original backgrounds would have been better.