Definitely needs some lighting in there, maybe incorporated with a ceiling fan? After that, how about a pool table or a card/game table with comfy rolling chairs?

Is that wainscot in the dark back area? My thought would be to move the TV between the windows where the chair and clock are. That way your FP and TV aren't competing for attention. Pull the sofa forward, centered on the two windows and TV, angle one chair where the TV is now and let the other one flank the FP facing the TV. In the back area you have room for Ruth's suggestions and could also build in bookcases and use it for a study/library/cards/game space. Lights, please!

Lighting is key for making this room feel much more comfortable. Table lamps and/or floor lamps.

Add some window treatments. It will soften the look of the space and take up some of the wall space (Less pressure to find art for the walls! Score!).

Consider bringing *at least* the leather chair away from the wall and creating a conversation cluster with the other furniture. You may have to play around with different configurations to make it work with the fireplace and the tv.

For that back area, I agree with decoenthusiaste and Ruth.