About the overworld, well it is nice, but.. well, these lines bother me. Not sure why... what lines, you ask? These lines:
Also, it is nice to see decoration, but I suggest you to remove some of them. Just my opinion.
About level 1.. the dirt is a light orange-ish. But when you enter the level, it magically turns into green!
Anyways, it really reminds me of other kaizo hacks, but that isn't really a matter for me, cause I suck at making creative puzzle things too. Also, I love the difficulty here! While not having too much use of glitches and pixel-perfect stuff, it has nice ideas here and there, also it is light-hard. Definitely for me! Oh, by the way, you should add some decoration, it is pretty flat now.
Also, I suggest you to make a tutorial level for custom blocks, cause it may be looking like something else, and can confuse others. You can do it, cause you know everything about it, but new players proably won't know it. Just a suggestion.
About the switch palace, it is nice looking. Nice on-off tricks here and there. A bit puzzling too, but not much to say about it.
So yeah, good luck!