See, this is a fine example of what I've been saying. I, unfortunately, have never read Discworld (although I plan to correct that soon). I have no idea who these people are, and no emotional attachment to them one way or the other.
But I can look at this piece entirely based on it's composition and style and say this is a great piece! I like the clean lines, and I like the poses. Even though this is not an "action" picture, it still seems like a moment of dynamic time frozen. I expect the figure on the right to say something (maybe a bit snarky, maybe a bit caustic) to the person on the left, and I expect the person on the left to immediately fire back a suave, snarky put-down in reply. It's almost like they've taken a pause to marshal their thoughts.
Again - thoroughly enjoying everything I see here!