There's no exact answer in how to compose this photograph. In my personal opinion, this looks like a "well thought through snap shot". There is nothing wrong with that, but it has that snap shottish look. (please understand that I have nothing against snap shots, they have their purpose, but imo not really in good photography). Is this a portrait?
What would transform this into something interesting, I think, would be if your son was sitting looking into the sunset. Also, lowering your horizon a bit. Imo, your son here should be an element in a sunset shot, not the sunset an element in a shot of your son. That's what makes this a snapshot atm. Reducing your son's role here, by lowering your horizon and having him look into the sunset would perhaps convey a greater feeling or emotion. As you ask, here's what I would have done differently:
- lower the horizon, making the sunset the subject
- making your son sit and look into the sunset
- place your son left in frame, having him watch into the frame and toward the sunset (I believe this somehow would balance out the shot, angling it from the right, having the boy look right from the left)
- find a location with less bushes, making the final expression a lot cleaner
- actually, I'd try for a few silhouette shots as well (meaning no flash).
- if you're able to, take your flash off camera and angle it somewhere close to your son. Also, diffuse the light to make it less harsh (less clear shadows)
Not sure if you want it, but a tip when shooting silhouette shots is to not let different silhouettes blend together. Meaning, having a silhouette of a boy blend with a silhouette of a tree, or two horse silhouettes blend. We want to see what the silhouettes are, generally, and having a clean look.
That said, I'm sure this image will be a nice memory of your trip :thumbsup: