There's not really a whole lot going on in this drawing, but right off the bat the three components don't mesh very well. You have a blocky dude with some basic shading and some cartoony proportions with light shading, in the back a svelte looking shadow creature and then a photograph for a background, there's no unity here and the work suffers for it.
As for the individual components, the dude in front's biggest issue for me is the inconsistent shading, you've put some shadows in, such as the ones from his hood and under his lips, but none under his nose, earlobes on his sweater or anywhere else. Also being slapped in the middle of the page like that and having his head continue up most of the page makes for a very symmetrical and boring composition.
Other than not fitting with the dude, your shadow guy is just sort of there, he's not interacting or even looking at the dude. With shadow people, especially skinny shadow people like that all sorts of opportunities pop up for interesting was to shape them and have them interact with normal people. Other than that there's not much to say about him since the head on, bust composition doesn't really allow for too much.
The background is a weird choice, making the sketch of the current drawing the background to the final can be an interesting concept but here it isn't really utilized at all. The problem here is that your dude and the shadow guy are almost completely blocking out whats behind them, so it doesn't make any sense, it just looks like they're standing in front of a mostly blank white photo.
I think if you want to stick with this sort of head on bust composition you really need to learn to render the characters better, and throw in a lot of details and shading to compensate for the lack of dynamic motion in the composition. Barring that what you should do is look into dynamic compositions in order to better create interest, things like the golden spiral, rule of thirds, diagonal line etc. Also look into body language and consider the personalities of these characters going in your drawings and try to make all that translate through the poses and interactions between the two. Hope this helps in some way.