I can’t say that I’m too familiar with Wario Land 2 and Wario Land 3 other than that they are really well animated games and have good reviews and great sprites.
There’s not too much in terms of rom hacks. It looks like there is a Master quest romhack for Wario Land 3 that rearranges all of the areas to provide a new experience. Persoanlly thinking abotu Wario Land 2 and Wario Land 3 makes me wonder about the different versions of Gameboy cartridges. There are the grey, black and clear cartridges. And I’m kind of wondering what the difference is.
Specifically I know the gray cartridges are for the original gameboy. So the only graphics are the ones included are shades of grey/green. The gameboy color attempted to automatically create palettes for these games. Then the are the black cartridges which work both on the Gameboy and the Gameboy color. I suppose that these are games built to the specs of the gameboy, but also have color data defined. And then the clear color cartridges are likely games that are built specifically for the Gameboy color, which means they probably use more RAM and VRAM.
In general I wonder if there is any difference between black and clear cartridges. Specifically it looks like a colored ROM hack would basically be a black cartridge and a ROM hack that added more sprites and took advantage of the extra RAM would probably effectively be a complete gameboy color port.