I think you’re getting some very expressive lines that remind me of Japanese prints and the brush work in classical painting from China and Japan. (Definitely seek this sort of thing out if you haven’t, it’s so much fun and very inspiring)
I love the use of brush pen and thick lines in these drawings. You manage to convey a lot of expressions, even with good line economy, and the poses are fluid. I particularly like the drawing of the man with a stick on the second page. The strength in the pose really shows through and the slight tilt of head adds a lot of character and confidence.
I notice that in some of these drawings, the hips are a little narrow. Perhaps a few full body studies or even studies of just the lower half would help if that's a problem you are seeing consistently.
Using brush pen gives you a lot of room to use line weight as part of the composition. I can see this is already coming into play a bit with the creation of shadows and deep patches of contrast so you clearly have a knack for the material.