My (WIP) Tileset, Please Critic Me!, I Need to Improve

[Kendaichi]

This took me 2 days, its a mixture of a 16x tiles and 8x tiles. made in Good ol' Paint!

There are 3 sets, all are incomplete, but i put them together so you can give me tips.
1 of them is gameboy styled (it also shows a quick recolour), the 16x16 one im trying to go for a Snes look, i dont know about the 8x8 one at the bottom, i just did that for fun



PLEASE tell me what im doing wrong or oddly!

Thanks!

-Kendaichi!