I think if there was some definition on the sides of the planks which make up the bridge, you'd get a better feeling for how solid they are. At the moment they look pretty flimsy, like paper.
I absolutely ADORE the waterfall, it's amazing. I'm kind of sad that the rest of it seems a bit dirty from the lines. Not sure how to explain it very well.. Oh wait no I do. The black lines everywhere combined with the low contrast coloring make the actual forms of everything dwarfed and underplayed. Those lines are your friends! but they're taking advantage of ya right now. Tell em to back off, start adding some color to them to put them in their place. They're great for establishing visual priority, but its like a where's waldo page fulla waldos. Also, the rocks are a bit light and contrasty? rocks look much better in my opinion when their lightest is a noticeably muted gray. hey I'll try an edit
...
Alright an hour of fiddling later : D well my edit didn't go as far as I'd intended, I brought it back closer to home to keep your nice aesthetic

First I tried to make everything pop more, break free from those lines, but keep em where they were good. Mainly on borders you want to push out from the lines because there were a lot of places where a single line masked the interesting contour of the trees and stuff. So push out there! and on the insides of object, lighten up the lines, color them, because otherwise they break up the continuity of whatever they're on. The hatching in places is kinda messy. Like WM said - more flats! flats are delicious and pleasant to look at. Then when I was done with that I noticed it looked completely way too saturated. Like it was a different time of day, but its in the forest, so I brought it back down to the same kind of dimness of the original.... but it kind of killed the rock entrance
here's an animation but gif sucks for 32bit color edits

I hope you can pull at least something out of this critique, haha. I like this! I want to see more screens.

EDIT:HOLY SHIT ITS A FACE !