Hey! I really love the work. I go NUTS for dark themes. I like the subject matter of your work a lot.
I think it shows through that you have talent, and you've probably been drawing for a very long time.
One thing I might say, is that in pixel art, more is not better. It's great that you've shown that you CAN noodle around in massive amounts of small detail, but that's a skill better saved for pencil and paper!
That being said, here is what I think you could keep in mind.
1- simplicity, both in the number of colors, and the scale. Great pixel art is simple, which doesn't always mean small. But, seeing how much you can say with the fewest number of pixels and colors is great practice.
2- an artists ability to "see" is just as important as his or her ability to draw. They're two sides of the same coin. They develop in tandem, there is a cause and effect relationship, but KNOWING this and focusing on it can help you greatly. I think it shows through that you're SEEING the information, but it's another game entirely to keep going until you KNOW your work is "there".
A famous painter named Richard Schmid has suggested that a Masters secret lies less in practice or talent, and more in their refusal to leave anything that looks wrong in their work.
I hope that helped!