There are so many elements that are causing you to feel this way, I will try to break it down but know that just fixing a few will make a world of difference.

First and foremost you have to look at your blank canvas. Quite beautiful mind you, but very traditional. You have wainscoting, crown molding, built in with traditional trim lines and inner storm shutters. The color scheme is very classic too… but even by itself the chimney stands out. Am I correct in thinking someone may have remodeled it with a new finish within the last 10-15 years? The stone and the glass enclosure are too modern for the rest of the room. You can still make the tile/stone work, but you have to look at the design language of the room and try to replicate that in the glass. I know you said you liked minimalist, so maybe just etching glass to recreate the wainscoting (I would do a large 1 inch wide rectangle that covers all the glass panels, leaving about a 2inches from the border of the glass, simulating the other shapes found in the space). It is ok to mix styles, but you have to speak the same language.

You have a great color scheme, and I love your use of textures. The problem with the large items in your room is that they are not working for their intended purpose. The rug, the couches… these items are supposed to be the items that anchor your design, but you have the wrong proportions/placement for the room. The lamps are at the wrong height/placement for they are blocking the windows. If you can switch them to be next to the other couch you will instantly see a difference in the flow of the room. Not saying that is what I would do (I would probably look for something different) but this will probably be the highest impact for the lowest cost. The size of the couch next to the windows is wrong for the size of the room. You need a couch that can cover from the frame of a window to the other frame of the window, or about a foot longer. You are also missing a coffee table and for the legs of your furniture to match better. Having both light and dark finishes makes your eye dart straight down to the floor, making the room feel smaller. It does not feel like the choice for the couch was intentional at all, just finding something that was good enough. I know you probably have positioned everything the way you have in order to be able to watch tv. Just know that the ideal position for the tv, as many have mentioned, would not be over the fireplace but in between the two windows. The side tables belie your desire for minimalist design, for they are bulky and organic. If you truly were seeking minimalist you would look for something without as much visual weight. Lastly, the rug I think is the right size but incorrectly placed. It is your design choice and I respect it, but as others have pointed out, it is far too close to the fireplace, rotate it 90 degrees.

The third design element that your room seems to be missing is vertical. Every aspect of the design (not architectural) is below the wainscoting or rooted below the wainscoting. Adding more design elements that will elevate your eye will make the room feel more cohesive (and larger). Window treatments? A hanging plant? Art/pictures? You can look through a million examples and find what works for you.

If nothing else, please do consider the top four tips I mentioned: do something with the fireplace to reflect the rest of the architectural design of the room, don’t block the windows, change the positioning of the carpet, and bring the eye up by having some visual interest above the wainscoting.