I agree with Frequency about the girl looking out of the frame rather than into it, I really like the composition of the background with the creek and shallow depth of field, I think the image would be great if only she were facing the opposite way, also I think she is looking too high up, creating an un-easiness which takes away from the calm, comfortable feeling the rest of the elements suggest. I don't think a heavy crop as suggested would do much good, as you would lose the sense of place and the composition would be boring.
I like the leading lines of the creek in the second two images, which draw your eye into the frame. I find its much more effective to have the lines converge at something of visual interest (like a waterfall or gnarled tree etc, rather than a bridge) Although the composition you've created pulls the viewers eye into the image successfully, there is nothing of interest to hold it there, or to make the viewer go back for a second look.
Your problem is an easy one however, while most people lack the skill of creating a dynamic composition, and rely on the visual interest of the subject alone (like people who only shoot skys at sunset and flowers.) All you need to do is find a subject that has interest, and use your skills of composition to hi-light it.
Using the 3rd image as an example. You've found an excellent S curve in the creek, wicked.. snap the shot. Now look closer at your foreground, is there an interesting rock near your feet? or maybe a cascade of water that is interesting? maybe a bush on the shore with nice colours. This is also why it is important to not include elements that may detract from the image, or confuse the viewers eye in regards to what they're supposed look at. (for example the tree trunks and horizon line along the top, or the tree trunks that sneak into both sides of the second image)
I suggest you keep shooting the way you are, and study other peoples work to see examples of subjects that really catch your eye, ask yourself why they're so eye catching and look for these things while your out shooting.
Hope that helps.
Joe