Well, I played through your demo, Ninni973, and here are my thoughts. I don't know how detailed you want this criticism to be, but I'll try to cover the basics.
Level 1Right away, I noticed quite a few graphical errors. Zorua Luigi is in the ground, the background has tiny specks and a green line on it, and the Kritter Goomba sprites are improperly programmed. As for the level itself, the building that I'm lead to believe is DK's Treehouse is very empty. Only a fleeing 1-Up Mushroom is present. I'm not sure why the water isn't swimmable, but I see that as a design choice instead of a problem. The bonus room nearly gave me a heart attack, and I had to make sure I wasn't bleeding from the chest. Anyhow, I finished the level soon after. Maybe it's just me, but I think it's a tad short. (Of course, my first levels were short, but I was a newbie then, while I'm sure you're more experienced.)
Level 2Right, so here's where you start showing your love for falling platforms. I actually like this level better than the last. Anyway, the same graphical problems are present here, which is to be expected, and the level's length seems about right, if a little short. Also, I like the purple background.
Level 3The main problems here are the two trips needed to complete the bonus room, a lack of reward for doing so, and most importantly, the fact that some of the level is impossible. To elaborate, that part you skip if you take the bonus is impossible, and if you're not Zorua Luigi, so is the room immediately following it. Also, the player shouldn't just warp out of the tree upon exiting the bonus. Use a pipe instead. The Kritter ambush section was pretty good, if short-lived.
Misc.THERE ARE TOO MANY MONKEY-FIGHTING TREES ON THE MONDAY THROUGH FRIDAY WORLD MAP. Also, you should add some music eventually. Oh, and the test level is intriguing.
ConclusionI'll be honest with you, your game didn't meet my expectations, and there're many problems with it. However, it's clear you've put effort into it, and that's all that matters. As long as you're willing to better yourself and keep going, you'll create amazing levels. Take it from a five year veteran who's practically seen it all.
P.S. I'm glad I played your demo, as well as helped you find yourself.