...To be entirely honest, I think that this story contains far too many clichés. As this subject seems to have already been beaten to death among your reviewers however, let me explain it from a different point of view. Your main problem is that you don't explain: You have all of these different heritages and powers just pop out of nowhere. You should take some time to explain where all of these things come from. For example, how is he related to Gryffindor, Slytherin, Merlin, etc.? Where does the "new power" from the beginning of the story come from? Was his magic being blocked, was it an inheritance, etc.? Explain why what happens, happens.
Along the same lines, you should also use a lot more descriptions in your writing. For example, you can take this "The house was massive, though smaller than the Potter Manor. It has a great round turret on all the corners, but was only five stories tall." and turn it into this:
"The gravel crunched beneath Harry's boots as stalked up the road toward the Davis' home. Though smaller than the Potter Manor it was still massive, stretching five stories into air. Thick, round turrets protruded from each corner of the building almost giving it the appearance of a castle. There was a strange, oppressive heaviness in the air that was only increased by the storm clouds gathering in the air above."
I guess what I'm saying is that you should take the time to fully describe Harry's surroundings, his actions, and the people that he's with. You'll find that the quality of your writing will increase drastically if you do.
The only other suggestion that I have is that you should take Harry's relationship with Fleur a little bit slower. You literally had the two of them look at each other and fall in love. At least take some time to let them get to know each other and feel a bit of awkwardness with the situation as they fall deeper in love. Use your own past relationships as a reference.
Keep up with your writing though! I've found that the best way to improve your abilities is to just keep on at it. Without even realizing it you'll begin to notice yourself getting better and better. Good luck with this story!
--B.I.