The most noticeable thing is the small amount of detail on a huge space. There's no reason to make the pages so big, especially if there's not much going on in the background. It draws attention to the emptiness behind the characters. The panels that feature just one guy talking can be vertical.
Like in this page
with an empty forest path it looks like sponges on a green liquid. I'm not great with trees and bushes but you might want to give the contours shapes of round leaves and grass blades. I would also add some stones or twigs on the path here and there.
...Of course, I also suffer from the lazy background syndrome and I'm trying to cover it up with crude polygon tricks so... yeah
But at least one panel should show the new location in detail. Like the one you put on your main page.
As for the characters, I can't help much since I'm not da Vinci myself... When you try do draw them from angles, it helps to sketch them out as blocks and cylinders to avoid stiffness and errors.
And I think you're being shy with the shadows. They are ok, make them a little bigger!