Dark brown paint can make a very dramatic and warm impact on a specific space. It almost reads as a dark wood.
To delineate a fireplace, I painted the entire wall it was on dark brown and it created a great effect. I used Ralph Lauren paint but will never again. It was the worst quality paint I have ever used. It was runny, smeary, and very difficult to work with. I would recommend either Behr or Benjamin Moore. A good dark brown color from Behr is called Melted Chocolate 250F-7. You can get it at Home Depot. Benjamin Moore makes a very similar color called kona AF-165. you have to go to a specialty paint store that carries Benjamin Moore for this.
If you're going to go for it, I would recommend only painting one area since it is such a strong color. Use it to highlight some architectural detail (such as what I've done with the fireplace) or to delineate space. It would also work well as a color for details (such as on a stair handrail, window frame, etc.).