That looks really "serene", I don't know how to say it, just very peaceful.
I agree that the tree could be thicker but I love the way it "flows". You don't even need to replace what you have, just add a "trunk" and when the moss fills in, it shouldn't really matter that you added a piece.
I think it would be cool if you added some stems with fine leaves and trimmed a few "bushes". You could add some color then without messing up the scale. I really like the colors in the earlier pictures but your layout feels more "real" now.
I do think it would look nicer if you leveled the substrate on the front glass. Other than that, I really like this tank. It's a different take on a few different styles.