In my experience, Composition is often thought of as something separate to value, and while the two are different, they are so closely intertwined, that you simply cant do one without thought to the other.
Composition is not difficult. Its essentially placing elements in a scene and leading the eye to them. Whats the story?, what do you want the viewer to see and how will you get them to focus on it.
Along the way you have to visually balance things out, but I have found that if you have a strong sense of value, you can create a far more compelling piece of art with simple composition.
The thing with photo's though is that the camera is simply recording whats in front, its up to you as an artist to interpret the scene and tell a story. So if it looks good in a camera and your not getting something similar in your paintings, its probably because of value.
Looking at your paintings, I would say the composition is fine, but you are really lacking in any real sense of form or lighting, in other words, value.
Check out James E Reynolds, one of my favourite landscape painters. The guy could handle any complex scene through a strong sense of value and composition. You can never go wrong to study others.
I know this might seem like a long way round to get you what you want, but honestly there is no other way if you want to get better. Just keep at it, keep the study going. If you enjoy waterfalls, keep painting and doing what brings you happiness. best of luck.
Edit: I done up an example to give you a visual idea of what I am blabbering about, using a quick sketch and then a thumbnail of value only. This is the normal way I work. I Get an idea, quick sketch, and then explore value options until I find something I can work with or fits the brief. Thumbnails take about 10 mins or less, and I usually do around 15 before I commit to something. You should try to do the same before starting to paint. Hopefully you see that value is integral to composition.