I think once you paint or stain the brick white the mantle will really stand out and look like a rustic and more farm like feature. Is that the look you're going for? If so then I would wrap the beams on your ceiling to match the fireplace mantle. I would think about lightening the color of all of them though. Also the mantle looks high to me I would lower it. The space to the right of the fireplace looks painful to me. I would think about taking that fireplace mantle beam across and then adding a couple more to do shelves down that side. I think the main issue with that fireplace wall is it isn't balanced .Explain that tile again. Are you placing it on top of the hearth (now brick)? Or on the actual floor surrounding the fireplace? Either way I would eliminate the tile. I don't see any need for it. Are you or did you add the window? It looks like it hasn't been finished with casing yet. What color will the casing be?

@ Mike Lipsky- sorry im just seeing your question. we love our fireplace in master bedroom. sorry im out of town on business so dont know height of oir fireplace but i do know we’re very happy with height we selected. i do know when we were considering what height for fireplace, we took into consideration view of fireplace when seated in bedroom chairs as well as when in bed so we could see lovely gas fire flames. would love to see a picture of your installed fireplace

None of these mantels shown in previous examples will work as depicted because your mantel will be much higher due to the way the fireplace is designed. So I do not see being able to use a mantel as an option. Cover it all with stone floor to ceiling like the example below: This mockup shows your existing stone floor to ceiling, which you probably won't be able to match. So you may need to remove all the stone and start over. But you can cover the black metal box more like you see here. Any mantle would likely need to be about 12" above that top vent to meet code, which is just too high for a mantel. The current mantel is not designed properly and appears to be a stock size shelf someone just hung. It is also likely not up to code. If you could use a mantel, it should wrap around the fireplace. But again, it will be too high.

Love your tile. I'd use the light neutral background color of the tile for the walls. How about the green for the mantle?