bye
Picture 1: All you can see is a flat rope and a Koopa. Try to pick a different level for the title screen.
Picture 2: Overworld looks pretty good, but personally, I would pick a different name for the house. Try telling whose house it is.
Picture 3: I know it's the beginning of the level, but try to mix up the land a bit. Put a bit of a ledge for the bridge to attach to, at least.
Picture 4: Not bad. Nice choice for graphics.
Picture 5: Still pretty good. Do you need to use the pipe to continue?
Picture 6: All just clouds? At the very least, give the cloud platforms some length. A good idea would be to change what the platforms look like and make some of them ledges.
Did you do this all at once? It looks like you started to get burned out at the end. If you end up doing something that looks like it would be repetitive (picture 6), go back later and change it a bit. In fact, a good rule of thumb is to wait about a week and take another look. That way, you can look at it with a fresh perspective. If you still can't find any improvements you could make, it's good enough to make your final design.
Current Projects: "Legend of Zelda: Balance of Power" (A Zelda Classic quest)