Wow that's pretty good. The arm holding the sword is especially well rendered. Three things, though: don't use black to shade everything. This messes with the perceived depth. The knight seems to be standing right up against the dragon, which may or may not have been the intention. I'm guessing, since he's looking straight forward (yet the dragon's head is in the top left), that they are some distance apart? If you use solid black to shade everything, it gives everything the same atmospheric weight. The two figures seem to be pushed up against each other in the foreground. Heavy, black shading (combined with the strong highlights) also suggests strong directional light. But since there is no strong light source nearby there is no need for it. It also causes your colors to look a little muddy, which is the second issue I wanted to address. Don't get stuck using only local colors. For example: the mountains in the background are shaded in gray and white, because mountains are naturally gray, and snow is naturally white. You have to consider how the lighting and atmosphere will modify these colors. If everything is done in local color, it reduces the perceived depth. Lastly, the rain. I love how you enhanced the mood of the drawing with rain. But you should be careful when using a lot of visual noise (like rain, dust, smoke, etc.) as it can crowd the picture and be distracting. What I suggest is using convolve (or blur) to make the rain "fade out" of focus near the edges of the picture. That way, the eye is still drawn to the main figures and not swamped with small details.
You're probably wondering: HOW CAN YOU WRITE THIS MUCH AND STILL GIVE IT A 4.5? Because, overall, I still think it's a great drawing and I can see the work that went into it. Great job.