Looking at your sketch...I like the gestures and I think the concept is great, very hard-hitting/emotional (I like that!) I think what I'd like to see is just a little more storytelling....the oar reads as an oar, but what is that other item - a shield? Part of the boat? Could there be some more items around that tell of his struggle against death, perhaps? eg an empty water bottle, food supplies all gone, a diary...parts of a shipwrecked boat perhaps... I get the impression that you want to keep the composition tight, with the relation between the two characters the main focus...but I wonder if you could tell a little more story with the details, even while keeping it as a spot.
The other thing is, I don't know if you skewed parts of the sketch in Photoshop but something is bugging me about the perspective of the characters...the way the lower parts of both bodies are bigger and the heads very distant...even though the faces/expressions are the most important thing holding the piece together. I'm not sure what to suggest, apart from it might be worth trying a few other perspectives, if you don't mind exploring other options. I kinda feel like I'd like to see Death's face a bit more clearly, as if we're almost looking over Willie's shoulder (or rotated a little more that way)...might make us feel like we're in Willie's position, seeing Death beckoning to come closer...At the moment, we could take either side (Death or Willie, it's quite equal in that sense). Hope this is making sense....
This is sounding like a lot of critique but please don't think so! I don't mean it in a negative way, it's definitely going to be a great piece and it's only because I know that your drawing skills are so very good indeed, that I think you can push it further before going to final. And of course it's only personal opinion, you can ignore it all and go with your first sketch if that's what you want Will be great to see how this develops!