What is required for an image to feel pleasant to look at? It's definitely the question we ask ourselves most as artists. My example illustration is certainly missing a beat or two but there are a few areas that we can comment on.
Depending on the story, we're going to want the viewer's eye to do certain things. Let's bring the viewer in and engage them in the action. We do this by following rules of composition, mostly.
The eye wants to take a journey. It wants to move from the main point of interest to check if there is any more information it can take in, but it has to go back to the main point of interest, because that is were the action is.
The action could be the look on a warrior's face, or the prize in the hand of a hero. It could be many things but it's got to engage us emotionally. Put us on edge, or put us to rest, somehow.
You don't have to follow all of these rules to make an image engaging, by the way. There are rules just the same as there are rules in other subjects.
Interesting things happen when we break rules and constraints in clever ways. But how are we going to break out of the constraints if we don't even know about them in them in the first place?