What geographical area? Is the shiny stuff insulation?

The window is facing north east, yes the shiny stuff is insulation and we are in Quebec.

The shiny stuff is vapor barrier and the insulation is behind.

We had a similar situation in our mudroom. We applied "gripper primer" and then painted it white. Since it's the mud room we didn't really care to sheetrock, etc.

Thanks for info. I think I'd install a remote-read thermometer and humidity gauge to see how it does this winter. Then decide.

What is this room used for--office, work room, ... ? Honestly, it does not appeal to me in the least.

I see the fan in the window. If it is a heated space, sheetrock, paint, perhaps shiplap ceilings and then there are a multitude of uses for the space.

Depending on the look you are working towards. Tongue and groove ceilings are nice with painted drywall on the walls and custom wood trim. I would leave the beams exposed and keep the wood a light wood and finished with a clear finish. Be aware that a lacquer finish will turn the light wood yellow, poly finish will not.

apple pie makes a good point. Barring any cooling/heating issues, I would dry wall, and leave the beams exposed, if possible. The floors look good. I recommend getting a cool chandelier to suit your individual style, and an area rug. Aside from that, what do you need most? Guest bedroom, home office, artist retreat, play area for kids, library, space for yoga,, music room, media room. Some of these can be combined, so I would try to make it as multi-functional as possible. It could even double as a large dining room for family gatherings. Example - inexpensive tables that are flush with the wall (for artist projects, whatever). These can be pushed to the center of the room, throw a nice tablecloth over them, and instant dinner party.

I'm curious what the stairs look like that lead to this room? An open staircase? Loft Style? Narrow staircase from a small closet? Also, is this a second floor or third? I agree w/ Lovelyv that once you rule out any possible heating/cooling issue, the room could be whatever you need it most for...but I'm thinking media or office or playroom. Great space!