This shows some real promise! I do however agree with what Mineyl says
Looking through the video;
0:09 - I assume those are munchers? Is there any reason we have gold and green ones? And aren't they a bit much for a World 1-5? Or is your hack supposed to be on the difficult side?
1:06 - What is the point of the star? The next area doesn't have enough enemies for 1ups... it seems a bit pointless really. Ironically, I think its one of the best parts of the level (without a a star of course)
1:33 onwards - The blue breakable blocks seem like they have nothing to do with the level. Putting them there just slows you down, they don't go with the rest of level (unless they can be used elsewhere that the video doesn't show) and clash with the rest of the (frankly brilliant) pallette
I really really like the level design though. I like how the first half was relatively flat and the second half mixed things up, and OK I moaned about the munchers, but they're not what this level is about.
Looking forward to seeing more!