We have the black mirror splashback. We love it and it soooo easy to clean

Is there something in the room you want reflected back that you love looking at? If not, why don't you find a nice piece of art work for the fireplace so you have something to enjoy rather than looking back at your other wall?

I feel it's too heavy looking for your room. You say it's a very large room, so you don't need it to make the room feel larger. Perhaps look for a picture/painting.

Everyone has some valid points and so I would also recommend moving the clock to the kitchen wall and place the wall unit under the mirror. Centre with the table with the additions of some artwork each side if the clock with wooden frames to match the clock. Find a low piece of glass or pottery or a runner to tie in the grey shades. I presume u have a grey lounge suite. Change the lighting as to what was suggested by People Space ARchitects.