I personaly don't like jumps were you are locked in a curve it's makes them annoying to land...
That beeing said your concept is great and the idea with a mix of 2D and 3D to avoid or do differentchallenges is very nice. After the transision the camera and the sprites sometimes bugged for me until I moved a bit and sometimes I got hit by 2D elements in 3D that should not have hit me so I didn't make it past the spikey crushers