I instead of having both 2D and 3D, focus on just one, unless there is a strong connection between them. The 2D platformer is okay, but 3D is not good. So just focus on one and make it really good(like adding audio)
The next step is to have a strong connection with theme. What makes a place strange? Maybe blocks can have special function, like red floor makes you jump lower and green floor make you jump higher, and you can make some fun level base on this concept.