Sofa too far away from TV. Bookshelves look odd with the gaps by fireplace. No drapes.

You need color, softness and more seating options. Add some colorful throw pillows and two small accent chairs facing the couch under the window. Consider changing the coffee table to a large circle ottoman or two smaller square ottomans. And I love all your house plants, but I would take down the 2 up high on the built ins. They are drawing attention to the rest of the empty space up there and that makes the room seem more empty.

The built-in is beautiful. I have never seen an application like that. Unfortunately, it only accentuates the vault and all that wall with NOTHING. SOOO much wall and really nothing to be done with it. Interesting visual--your clocks, but I think they would make a bigger statement if displayed closer together. To me shelves are for books--mostly so I want to see a few of yours with some books, just because that is expected. The larger couch does appear to be too far away to really watch TV from. What is behind it? Is that a wall? Perhaps moving it in a closer L with the love seat would cozy things up and give you a new space for a games table or sofa table?

Definitely float the sofas, it will make a big difference. I would not put anything on the wall above the built-ins.

Curtain panels would help but it looks like the corner window might be too close to the built ins. I agree about floating the sofas to make the room look more cozy.

It looks like you are using mostly overhead light which can be harsh and shadowy. Adding lamps will also bring warmth.

I would use the red from the rug and get some large red accessories - pillows, vases, paintings, etc. Place them on your coffee table, in your shelves and on the walls.