I see a lot of good design principles that are let down by poor execution. You definitely have a sense of what kind of challenges are germane to single player — respectable enemy placement, some precision platforming, triggers, collapse scenery, and other such things — but it’s all done way too quickly. The running section (you should know, btw, that fast feet events don’t actually do anything in JJ2) is ended by a wall which signals that it’s dangerous once again and there’s an enemy coming; that’s a great touch. I see tiles being used for specialized purposes, and definite hints of JJ1 design philosophy (e.g. the secret level hidden behind the end of level sign). As PJ said, you just need to spend a lot more time polishing your levels and making the good ideas that you have more appealing to look at and play. Choosing different tilesets will also benefit you tremendously. Inferno is difficult to use even for experienced level designers, and the other sets you used aren’t really very high quality. Find a nice good-looking, easy to use set and see if you can’t find some inventive graphical tricks to complement your level design intuitions. Keep it up.