Hi Linda. You could paint it and the wall behind your favorite color. You could add some shelving or a mirror above, or you could tile, or add stone to it.
I would put an oversized clock mounted to the wall. Eye catching item everyone will check for time!
I would invest or make a really stand-out wreath for the big blank spot over the fireplace opening. (Please hold the thought as to, "Is this a potential fire hazard?" Adding fairy lights on the shelf is a dramatic game changer. It will knock your socks off. You can weave the lights around the items you want to display. Add a little artificial green stuff. Change your motif to fit the seasons. You have lots of potential there. And, check out "Pintrest". (Definitely needs a mirror hung about two feet above the shelf. Don't get one of those monstrous things.)