The first thing I would do is hide the wires! Wires are always and eye sore! If you cannot do this yourself, hire a professional to fish the wires through your walls and into the cabinet to the left. This will tuck them out of site and give you a much cleaner looking space.

As for the mantel, you are heading in the right direction. I like the large lantern on the left. Having a large item on the left helps to balance the weight of the TV. I would move the candles currently sitting on the right, your best bet is to focus on the left and leave the space under the TV bare. It is a short space and you will only be able to put small items there, which are going to look even smaller underneath the large black square of the TV. Hanging a large mirror above the built in, behind the lantern will also help to pull your attention away form the television. Think layers, and height gradations. I would add a few more items on the top next to the lantern, but work in something high (the lantern) something low, then something medium height.

Inside the cabinet your framed photos get lost. I would put books, baskets, videos. Things that are going to fill the space and cover the back of the cabinet.