I like a mirror over the fireplace, but I agree with the others, the one up there overpowers the fireplace.
I would put one up there that is the same width as the opening of the fireplace but tall.
Also, you need something over the tv to balance your wall. You have height to the right of the door, then something over the fireplace, but the eye drops down to the tv and makes the room look "heavy" to the right.
Since your clock is rounded, maybe an oblong mirror above the fireplace, and something in a round shape over the tv. Your picture under the clock is squared off as is the doorway, the mantle and the tv. With something rounded above each it would give the wall an arch-like appearance, and draw the eye my centrally to the wall.
I'd also add some of the rusty red that is in your rug, into the room. Doing so would bring out the color in the rug, and add some "pop" into the neutral. Tall candlesticks - of varied heighth - on the mantle with candles the same color of red. ( I have some in black & antiqued silver that I got at Hobby Lobby several years ago that would be great. They don't still have the exact ones, but they do have similar ones still) Maybe some pillows on the couch in solids and patterns with red and whatever other color that is in the rug ( I can't see it well from this picture). Maybe add some olive-y green if it's in the rug too. Maybe some smaller pictures or some type of wall decor, that will have bits of the red, the green, along with black and neutrals. Those would be easy to find.