I really like the concept, the message boxes in the intro, and the graphics you chose to use.
Nevertheless I have to point out some inconsistencies in this level, especially for this screenshot :
At this point, I've hit a blue POW and did not find the corresponding door; I got a powerup that is not designed to shoot the blocks located just next to it; and now I'm forced to die because I mistakenly fell in the water and the tiles are too high for a jump.
Also be careful with the colour set of these gray cement blocks, it is not in tune. You may want to create a new map16 tile for them, using a more fitting palette.
Same here, I fell in the water and cannot jump back.
If you want your player to feel good with his decisions, you may draw some pathes with coins, and if you really want a punishing death when one falls next to the right platform, do it properly, give no hope. If I didn't have the water at this spot, I would have died without that much frustration.
Also, this may look simplistic maybe, but the thing with P-switch is very, very confusing! The door colors do not match the P-switch colors, the door colors will change when I change sublevel (or should I say "go to the past", wink wink), some P-switches are found just upon entering a sublevel, next to another door...
I enjoy the concept and I trust this level will be good, but I think you can make it even better and more enjoyable with not so much effort.