I agree it is too big for that space. I suggest a horizontally oriented framed print. Very cozy room!

mpoulson - great minds think alike!

I would do a circle mirror or a long horizontal mirror. The mirror you have on there now is too small for the fireplace. The room is gorgeous!! Good Luck!

Mirrors must always reflect something beautiful or interesting, so this location doesn't qualify for a mirror.

something along these lines....depending on what style art you are more comfortable with....here is one example of an abstract and then a traditional landscape.
shop in some local galleries, or etsy, or go to your local college/university and see what some of the art students may have available. You may be able to commission one of them to paint something with some of your room colors in it for a good price!

Another alternative is to find 3 smaller pieces and hang them side by side!

Thank you all for your great suggestions and compliments! I really like your ideas, mpoulsom, especially like that first piece of art.

I think the shape and orientation of the mirror is fine. It's the frame that does not work. It needs a frame that is rustic / cabin feel. Try to find an antique mirror. I don't like the artwork idea unless it reflects the feeling of the fireplace.