I used to have this issue with stiff line art and why some of the things I paint or color with look flat. It's the issue of understanding 3D forms on a flat surface; it tricks the mind thinking it's actually real, or even possible to touch it.
Line art is something that will come out naturally as you draw more confidently and you understand the piece you draw behind it and one of the issue's I solved when drawing nice line art, is using my whole arm rather then my wrist to draw circles, lines and curves.
Secondly I recommend doing more figure drawing's to free your mind from certain restrictions. I wanted my characters to have life in them, so I use very quick 1-2 min sketches from posemaniacs.com/http://artists.pixelovely.com/practice-tools/figure-drawing/ or even regular people in photographs just walking along the street. Drawing from life is your best bet and trust me, it will be a little messy the first time, but once I understood why it had to be done this way, then I moved on to other topics like: Why do people draw 3D stuff? Is there a point in drawing 3D? What am I learning from it?
For example, I take the human figure that's made out of cylinders and cubes. Not just flat squares and circles; why? It's because in reality, we're all made out of three dimensional things, I touch my arm, it's round. I feel my face, it's made out of different forms like skeletal and muscles and not just a square or a triangle. This is to help not second guess where you are placing any object or limb in your drawing's- because being unsure where everything goes will definitely show up in your drawing's!
I also noticed your shading is going all over the place with no true source of light hitting on your character. The shadows are too consistent and the value's are not flowing correctly in their perspective direction. I understand you really like to work with gradients and so do I too, but you really have to work with flat colors and value's first, because your drawing's will look very muddy and not as nice as you want them to be. I believe that shadows and light should be taken great care of once the form and drawing is complete. With great subtlety and understanding, it will definitely push your drawing's look greater then what you have now. I totally suggest reading james gurney "Color and light" for the realist painter, I'm reading it now as well. It has great information about the principle of light and shadow, and why colors are the way you see them.
Lastly, my final suggestion is to do a study of more reference material. Because you're starting off with fantasy and anime right away, you have to understand that it's just a style- it's based off the real world. For example, the purple (dragon?) doesn't really strike to me as real to me, since the tail and the shoes needed a bit more care to them to really show their design. If you need help with animals, use their reference's and apply them to your drawing's- but don't copy the exact pose of it.
I really hope this helped and that I'm not trying to be mean or downgrade your art; you just need a little more bit of effort, persistence and study and it will show up in your next art piece. You have the skills for it, but make sure you are pushing yourself little by little, even if it takes longer then it should. It will look amazing at the end of the day!