to me a bit too much negative space at the top...a bit off the top gives you plenty still and the subject isn't quite as lost ... I would also consider cropping to make the lighthouse not in the center.
I think this could've been stronger if you had shown a bit more of the lighthouse's hill at the bottom of th eframe, so it looks more like the landscape and this tiny lighthouse jutting into the massive sky.
You have taken a pretty landscape but I'm not sure that you have a true neg. background but only surrounding the area with clouds. Think in terms of 'negating' the background by bluring or whatever bringing 'all' the attintion to the lighthouse (your subiect). Good luck in the challedge.