If you're looking to keep the brick looking like brick, a light white/grey-washing would instantly brighten the space. You could also get a big chunky mantel to put over the fireplace.

If you want to completely modernize it, you could go all white/grey and add some open shelving to the upper left and right!

Paint the spindles - they are kind of retro cool - but change the top cap to be a clear coated wood that matches the new floor (see below).

Paint the brick wall, but don't paint the concrete mantle/course that runs through the middle and don't paint the hearth/seat.

Install a very light - blonde wood floor.

Add a new wood mantle - keep it thin about 1.5" of face dimension and about 8" total depth that runs the full width of the room - set directly on top of the concrete band. Match this wood to the new flooring. Check to make sure that there is adequate clearance of the wood to the top edge of the fireplace. And if the heights work out turn the new wood mantle into the sill of the window on the left.

Are those coach lamps on the brick wall to the left and right of fireplace? Take down the lights if that is what they are and infill the two planes that the lights are on with drywall laminated directly to the brick. Paint this out.

Add a couple of strategically placed pot lights - two on either side of the f/p that are gimballed to highlight the new drywall area and one centered on the fireplace itself.

if that is a stippled ceiling then scrape it down and paint it.

Add furniture, side tables and lamps, an area rug, couple of pieces of art and some decorative bits on the new shelf and... you're done :)

Here are some more pics:

Tear out the brick. Drywall the sides, if it’s a wood burning fireplace, resurface the center hearth with tile or stone, if it’s gas, drywall it as well.

I love the stair rail and would suggest painting it. Also, I would white wash the brick and keep the existing mantel. Change the wall sconces and fireplace insert for something more modern. Paint the walls a light grey. I would also suggest a big piece of canvas art that has a geometric print, something modern to highlight the deco feel of the railing.

Just posting that I also think it's retro cool to keep those spindles. :)

Are those ceiling lights near fp wall? If not, new ceiling lights for brightness.

Flooring concrete wash or stain - polish it for sheen?