Paint it! See our solution here. http://creativemeinspiredyou.com/updating-an-ugly-brick-fireplace/

I love that idea. I can't envision it on this ugly rock. I saw your pictures.

I don't think the rock is bad, but I would remove the doors and get a new updated one or a screen. Add plants to the shelves.

I think the stone is great, it's the brass insert that's the problem. I'd advise against painting until you modernize the insert and see how that sits. I agree with Bailey, a nice piece of modern art, or some relief sculpture above the FP will work really well too. I'd do a big Nelson clock, or Nelson inspired starburst clock, but that's just me.

I'm not sure everyone is getting the ugliness. The color is sort of like wet cement. and the brass insert is going asap.

I think a lot of people just like the look of cement! :)

You might try staining each rock individually. Select several colors that are similar to each other as well as a single darker color. When you stain the rocks you would start with the lightest color. Stain the entire fireplace with the lightest color including the grout. Then add darker stains to individual rocks, skipping around as you stain them. Know when to stop!

But first... Remove the brass. You may be able to spray paint that piece black using BBQ paint.

My vote:
Remove the brick. Trying to hide something you already hate will be a waste of time and money.
You've lived long enough with it.
Just find someone that can help you with it.