bump

At quick glance, the built-ins look unfinished to me. Can you add a trim at the top (maybe similar to your window trim, or coordinating)? And maybe a similar trim style in mantle form for the FP? Are you keeping all furniture? You could consider layering a rug on to of carpet under the sofa to ground that area (but depends on how plush your carpet is and tripping hazard, etc)

I think what bothers my eye is 7 rectangles in one space (I included the mirror and picture, but you also have 10 additional rectangle shapes in your shelves). I would extend the bookcase to the ceiling, trimmed in molding, as gcubed suggested and, because I only see miscellaneous, small “filler” items on your shelves, you might use doors on the lower portion of your units, and accessorize with larger, and fewer items. I do like the sleekness of your fireplace and am having difficulty imaging a mantle, but maybe others have suggestions.

Adding a wood mantle is a great idea and in regards to bookcases, maybe consider cabinets and open shelving to match mantle. With the other bookcases in room, there is a bit of bookcase overload

If you do want something like the look below, make sure the bookcases reach the ceiling and have a trim for a more finished look. Really important as well is how you accessorize shelves and mantle and there is lots of on line help

When you reference help with layout, hard to suggest - is there any other location for sectional?

In regards to lighting, add lamps to side tables, a floor lamp located where it’s needed and if you don’t need the ceiling fan/light, replace with something that provides good lighting and also place on a dimmer.

You can get a lot of ideas by searching Houzz and Pinterest for inspiration, as it is hard to know how much you want to change.

I also suggest moulding and bringing the cabinets up to ceiling. If you can’t do that why not paint them a color? It will as more interest. I would also take everything down off the book case and the mantel area and slowly play with the pieces you have and group some larger pieces in. Is there
Room for a floor lamp somewhere? Also maybe do some art above the fireplace rather then a mirror. You could always layer some art together.

IMO you have nothing on the shelving now really worth display I would rip out the shelving and take the bricks to the ceiling and add a low cabinet on each side of the FP and hang art above them a much more updated look and IMO the FP as is is too tall for a mantel I think you have more bookcases than are needed and most of what is on the others could go in the new cabinets on either side of the FP

Unless this room is to be a library, I'd remove all the cheap looking book shelves. If you can remove them intact, sell them and photo the space again so we can help you design it. Is your sectional blocking a doorway? Do you have a second swoop chair so you could use them as head chairs at your dining table? How does the last pic relate to the rest of the room? Two lamps are all I see, other than an eyeball can on the ceiling. Put some money into adequate lighting.