this piece would benefit greatly from being a vector piece. Not to say that just because its big, but because the individual pixels serve no value to the imagery, quite the opposite, the rigid intersects of color are quite glaring, making it feel rudimentary and unrefined.
The subject matter isnt amazingly exciting either. I think that 'pretty things' like sunsets and rainbows truly do attract a lot of people to draw, but the only semi interesting thing about it to me is the clouds. Sun is dead center of the screen, the horizon is almost dead center of the screen, it makes for a very simple composition that wont hold or attract your viewers attention at all.
one last issue i have with your bold yellow choice for the sky, while its quite striking, ive never seen a sunset make the sky THAT bright, and without any gradation into any cooler colors it makes the sky look very hot/alien (like a sea of lava on mercury perhaps).
I recommend trying to get a trial copy of flash or some free vector painting programs available and try recreating this piece using those tools i think youll find the final imagery much more appealing while still utilizing very few solid colors to illustrate your scenery.