2 things come to my head I guess,
- The overall image is too blue in my eyes. Yes, you should have a set color tone, but it almost looks like you went Colors > Colorize and then added some purple shades.
- There's some perspective-stuff going on at Samus' right shoulder. Are the "balls" (the flying things) in front of the white clouds or behind them? The white splatters are in the front, but vanish behind the shoulder as well. This might be just my head messing things up though
- The background is pretty dull, especially the left side. I'd suppose you can add anything there and make it look better: your name, a fade-out, slight scanlines, cut the side off completely, I dont know
To me, it looks too empty there. Of course you shouldn't distract from the render, but you shouldn't leave it just empty.
Uh.... I guess that's about it with the negative things I can name