with small parts . Sorry, just culdn't resist that one. Try using a 30 cal. ammo belt. Cut off the bullet ends. Not sure if I am correct in this but I belive they were made of cloth, so you could heat and bend to shape and paint the cloth and the spent shells.

Generally looks quite good to me. Nice lighlights and shadows on the uniforms. Both faces look good. The hands on the guy on the right look lilke you used a wash that wasn't fully blended in, the other guy's are excellent, though.
As mentioned, the sleeves could have used some work. Minimally, a very dark version of the outer sleeve color but better to have them drilled out.
Leaf placement looks okay to me, though they are a bit flat. Fallen leaves tend to have a bit more curl to them. I've had to pick up far too many not to notice this. As you are planning, a bit of color variation in them will be good.
The trench walls look okay with adequate color variation to my taste.Adding some mud/water stains dripping down from the spaces would punch them up quite a bit, though.

Super job,Brett! The story is in the figures faces-fear,uncertainty,despair. You chose to use great heads for this and you did them well! The bleakness of the scene sets the mood. The equipment of war is typically 'German neat',orderly as it should be.
As others have already said, a little weathering of the leaves,the trench walls. Maybe some kit hanging from wall nails or knife. Trodding up the ground and alittle color variation. A 'lived in' look.
Too much and it distracts I think.Better too little. The viewer will be drawn to the faces,the story.
Now that you have your first one out of the way, how are you going to top this?
Cheers!
Rick

The only way I've found is with a lot of patience. Cutting off the rear and front bullet portions on a belt on an angle from top into bottom as the german belts had "fingers" on top ( if you look at a photo of an MG42 ammo belt you'll see what I mean ).

Then a long and patient process to carefully drill out each link with a .25mm drill bit in a pin-vice.