A noticable this thing to remember is that the reflection in the water would always be directly under whatever is in the sky. The eclipse reflection should be beneath the eclipse in the sky not moved over. Check out these photos here and here and here .
It's a good lesson in using resources and researching before even starting a piece. Usually you WON'T find exactly what you are going to paint (which is actually a good sign if creativity and imagination!) but if you look hard enough, you'll find something that indicates a process to use or a way to expound your idea in order to ground it in reality, no matter how out there it initially may be.
There's always room to polish our work so I'll just say to keep looking for ways to improve and it will pay off! Great job, Vicugna! Keep it up! 
I agree with the points DexRunner stated.
Try to study real life scenes and think about how you would draw or paint them traditionally. You can apply your knowledge of drawing and painting to pixel art.
And about pixel art related crits:
I think the clouds in the preview image look better. Try to use clusters rather than lines.
I liked how the far mountains have a blue atmospheric tint. And I am seeing some banding in the reflection. Try to avoid hugging pixels on the contours.