Hi, I think the brushwork, or markmaking, is definitely important, but its like the icing on the cake. For me, If the values aren't right, then the best brushwork in the world isn't going to save it. Now i'm no authority on value, its complex, but in your image the values seem wrong. The midground, the tree and shore, are the same, if not darker than the main characters. It just flattens the image out. If you desaturate them, reduce the value range, i.e don't use darkest darks or brightest brights, and use less saturation, it will increase the illusion of depth. Things get faded out the further they go away, basically.
I think the branch the monkey is hanging on is too long, it gets lost in the midground. The highlights on the main characters could be ramped up loads. I know its a jungle scene in daytime, so the sun is everywhere, but you are the artist, put the brightest bright where you want people to look.
One other thing, people tend to read images left to right. If you flip the image, it reads, monkey, tree, croc. Bit better for telling the story.