As was said before, the lighting doesn't match. For basic compositing use this checklist:
1. Feather your addition: usually you can just contract the selection 1 or 2 pixels, feather 1 or 2 pixels, invert the selection and then press delete.
2. Lighting and shadows: in this case you have backlighting but no facial shadows. Make sure shadows come from and parallel the light source. Use any burn technique.
3. Color: there should be a little sunset color on the subject here. Paint in Color blend mode.
4. Texture: No real problem here, but for demo I added a little noise that helps fool the eye. In extreme cases, you can use one of the two images as a source .psd for the Texturizer.
5. Focus: you may need to sharpen or blur either the subject or background so they match. I blurred the background for realism and to help blend in the subject with the background.
6. Fringes: As Isabel said, you can blur a little, but a better way, at least for this image, is to use the clone tool set to Darken mode. Set the source on the sky and run the tool along the fringe.
Bill

http://www.pbase.com/image/23237635.jpg
Steven S wrote:
> Any way to make this look more realistic, and less "pasted"?
> http://www.pbase.com/image/23233849.jpg
> --
> Steve S
> http://www.pbase.coogidsshyone/root&view=tree
> p-A
>
>