I have nearly exactly the same layout, except add a door in the upper left corner and replace your bottom wall with wall, wide opening, closet. My room is also longer than yours - it's 18'x18'. I have added Billy bookcases with the half doors and height extensions to either side of the fireplace. It looks good and the extra storage is a godsend. I would definitely integrate a desk into any built-ins you do, like the picture kellyeng posted. Obviously custom built-ins/bookshelves are nicest, but the Billys are fine if you are on a budget. You could buy the short ones and/or cut the Billys down to fit on top of the desk. I have found two layouts that work for my room. Obviously we have different furniture but perhaps reading this will help you. 1) float sofa in front of fireplace, put sofa table with lamp(s) behind sofa, put two upholstered/leather large chairs in front of left window, float loveseat in front of slider on right, put coffee table in front of sofa, place dresser for extra storage on bottom right wall. 2) Float sofa and loveseat in the middle of the room perpendicular to fireplace with coffee table between them. Put the two large chairs south of the sofa & loveseat, angled toward fireplace. Put dresser for extra storage on bottom right wall. My TV is above the fireplace since DH wants it there, but you can easily put yours in the upper corner since you have less furniture. I would recommend that, actually, since the closer you are to the TV the less comfortable it is to look up that high. You really just have to move things around until you are happy - at least for now. The room is awkward, no doubt about it. So, when I get sick of one layout I switch back to the other. I switched back to my Option 2 yesterday. DH laughs at me but hey, moving furniture is cheaper than moving.

Like you I have an awkward tv room with three double doorways, a fire place and two windows too. One thing that has helped a lot when entertaining is to have peripheral chairs next to my fire place aswell as in my three window sunroom. The side chairs are comfy yet light enough to easily pull near the main setting for football viewing, games or conversing. I would find some light yet comfy arm chairs to place in you lovely windowed nook. And a side chair or two beside the fireplace too. Move the tv a bit toward the kitchen entry maybe on an articulating arm mounted to the wall.

Could you split this room into two areas, couch (though this one may be too big) and tv in the window nook area and then a pair of sitting chairs near the fireplace?

How about adding some photos of the actual spaces and the furniture you need to arrange?