I think the outline on the clouds don't fit the overall style. Other than that, wow.
WOW! Woooowww, the shapes are so beautiful! Excellent job :D
- Very simplistic, I think you should still try new things, but this is nice : ) -
Wow I am highly impressed.. Your best work. I think you should continue with this style for a while and see what it can evolve into.
It was quite an effort on the AA side 
I'm not really into this kind of pixel art but it was nice to experiment.
As for the palette I agree that especially air element is maybe too monochrome.
This is amazingly clean! If I had seen this on an other site than PJ I wouldn't have recognised it as pixel art, looks like vector!
The palettes for the two pieces on the left side are vivid and have nice ramps while the other two are dull and lack counters.
Fantastic style! Love it!