Whatever you decide to hang needs to be to scale. A couple of very large canvases side by side, for example. I would not recommend a wall of small pictures or shelving. I would tend toward something more subtle in your art selection since the focal point of the room is the fireplace.

You might consider a solution like this.

The suggestions above are good. Although, you could wall paper that wall in something fun and colorful.

A very long piece of art that you love would be perfect.