The image has good composition but the contrast is too severe. this is probly due to not quite getting the exposure correct for the sky, but then again you are shooting into the sun so you are allways going to be battling with contrast. Or you have over processed it.
Did you use fill in flash on the tree? or a reflector?i agree with @noxer. about the horizon and contrast.
Thanks for the comments. I didn't use any fill flash or reflectors, I used HDR [gasp] :)