OH! You should be very, very proud of that. And the story behind the pic is just...I loved it!!
I should really look at this on my home monitor...
What part of this creation is your work, and what part someone else's? Your father-in-law has the "tired warrior" down pat. But I feel like he's overlit for the background he seems to sort-of be a part of. And the magic on the sword isn't quite right and the angle is funny.
Having said all that, the overall experience (both the finished cover and the story behind it) do make me want to read the book to figure out what's going on. From a marketing standpoint, well done!
OK. Now looking at it on something larger than my phone.
I have the distinct impression I'm looking at two printed cels layered over the background of stone/sky/grass. So there's the background layer, the father-in-law layer, and the text. Aside from the sword, there's nothing really tying them together. And, as said earlier, the sword doesn't quite work for me.
Lighting: I think he is slightly overlit overall. And the light on his back either shouldn't be there or should be a different tone. It feels, well, lit by a photography light, rather than a doorway or a sunset or a table lamp. Maybe it will tone down some in the printing process.
I'm glad you're doing these projects. I think it stretches your brain in a different direction. And it gets people excited about books and photography and actors and and and... you get my point.