Not a Pro.

Can you post pictures of the room with the wood floors? and your furnishings

So take the whole surround out including the book shelves which BTW do not seem to be holding anything worty displaying . Why the beans at all in that space IMO those make the ceiling look squat.

If I take out the surround...what do I do with the gaps in the flooring? And I am not a fan of pointless display items just to fill empty shelves either so I don't mind the built in going.

Paint that whole wall one accent color. I think that’ll help. It’s the choppy effect of the three different elements making it look squat.

Adding addition shelving sections above the lower bookcases could help by distracting from the length with the height at the ends. Then you would have a lot of shelves to fill.
Or take out the bookcase sections and rework the fireplace surround. Of course you would then have two empty walls which will want windows.
Maybe just add art on the sides and hang the mirror, with a framed family photo in front of either end of the mirror.

Rachel, like the mantel, built ins, shelves, walls, everything but the brick? One color? Or the brick too?

I would have doors made for the bookshelves and then paint the rest of the wall the same color as the built-ins. I think that would help make the whole thing feel less chopped up. At the very least, paint the wall above and behind the shelves the same color as the mantle and surround. Then limit the decor to just the fireplace. Instead of the mirror, find a piece of art that's about the same size as the firebox and put that over the fireplace with a pair of candlesticks on one side and a pretty piece of pottery on the other. Don't use tall candle sticks, use shorter candlesticks with taller candles.

If it were my home, I would add a box made of picture molding above the fireplace on the wall and paint out the area above the shelves in white to create a visual extension of the book shelves up the wall. It would be very simple and cost effective.

My apologies, paint out in the cream color you have now, not white.

I like it

This is what you can achieve with picture molding and paint.

I think you need some visual tricks in this pretty but very square room where everything emphasizes the long horizontal. My first suggestion is to cover the open shelves with paneled doors to supplement the verticals already formed by left/right edges.

Try angling your couch unit facing towards your bay window and curving to center of room, and make those windows a focal point with a pretty table and 2 small reading chairs. Emphasizing the windows would make the fireplace wall seem less conspicuous. An interesting pattern rug there or an oval one in front of couch would help to pull the eye down. If I seem to over do the round concept it's because round things force the eye in a circle. A really large 1/2 room sized circular rug extending under the couch would be a major focal point. I assume you have replaced the carpet with hardwood?

To narrow shelving wall, disguise it. And keep it simple with only a single focal point.

Consider painting everything in that area white, including wall and fireplace. On mantle only one to 3 items. With space above and below it an oval mirror might be nice, with family photos you mentioned along side. If you enjoy flowers, a full arrangement there would complement a mirror nicely. Keep the wall and top shelf above bookcases free. If you add paneled doors below, you could paint faux panels on the wall above. The more verticals and fewer horizontals you can manage will improve things immensely. If you keep the open shelves. remove 1/2 of shelves and keep anything on them simple. Books are always attractive and kids especially can benefit by books being easily accessible. Nicely painted panel doors would add much needed verticals. Photos and a few favorite items could be on tables in front. This final suggestion would require electrical work ,,, but moving the ceiling fixture back away rom the fireplace might also detract from the long horizontals.

Good luck with your decorating, and also with those sequestered kids!

If you just put in the floors, can't you get some additional boards to fill the bookcase gaps?

If the wood floor is new you should be able to get matching floor for the gaps

Brick and all- one color

I don't understand your photos ...with all the different furniture....which furniture is actually in your living room ? The mantle and the entire look depends on knowing this ...your should group everything closer to the fireplace to make it cozy ...and perhaps paint the brick in the same color as the built ins or in black to give you a cozy feel... You could , if you need more space for books use the space above each side to make bookshelves or photographs , paintings ..sculptures ...yes, and candlesticks ....but , you will have to pull that all together once you have the furniture in place ...in my opinion ...

I love built in shelves. I love fireplaces and books and surrounding myself with my favorite things. So I would leave the shelves and paint the wall and shelves.

BUT..... if you remove the shelves, one answer to the floor issue is bench seats. Like a window seat, but on a wall. A very cozy look.

I think entire room would benefit if you painted it an off soft white, including the bookcases and brick (Could go pure white on these). I just painted both my basement and living room stone fireplaces white and wish I had done it years ago. Made rooms feel so much lighter. Spray paint the brass grill and replace the ceiling fan if you can as It only makes ceiling feel lower.

Run some vertical beadboard paneling above the entire mantle and paint the same color as the shelves. Inexpensive, easy and will give you a seamless look instead of “squatty.” Please don’t paint the brick, it’s so pretty and warm and cozy!