more images of it:

oh, and sorry for those boxes next to the door, we just recently moved so there are tons of boxes eveywhere in the house! lol

An area rug, or rugs....

I love the third suggestion by GM Construction above - that's a great look - b

Thank you so much for the opinions! I specially love that second picture from GM Construction! What kind of color scheme do you guys suggest? Should I continue on the green-gray-black-and-white combo?

Also, I was thinking about putting another armchair on that reading corner, but I'm not sure on the color/style of it! What do you think?

Green/gray/black/white is on the eclectic side! If you don't plan to stay in this place long, choose art, rugs, etc that you will be able to use in your next place. You can add in other colors that won't be out of your current scheme. Use your favorite colors in the Iron Man poster and the mask to start with.

You need a lamp(s) close to the sofa for reading and conversation. I can't see where the electrical outlets are, but I bet you can fit at least one end table in that area. What are the space constaints in that area?

If you are staying for 2 years, you could ask the owner/landlord if you could paint a neutral color. They should be ok with anything reasonable. It would add some life to the room.

I think the oddball items in pictures 2 and 4 are what is wrong with the space. The sofas and the reading area and bookcases are fine, but the hanging fixture in the reading area is calling for a dining area or, if you already have one elsewhere, a library table with a chandelier above it to turn the space into a real library. Anchor it with a wonderful large area rug that can go to your next location and be used in the living area. Could be a great space for playing games and serving a buffet style meal. If you'd want to invest in something you'd probably leave behind, try building radiator covers to give a more "furnished" effect. I've often done custom upgrades to a landlord's property and then he has paid me for the items when I moved. Rad covers can simply sit over the rad and not be nailed down. You could even try making them with salvaged pallet wood.

At first my inclination was to say to move the bookcase to the end of your room. Put your two chairs and lamp facing the bookcases (backs of chairs toward back of couch) with the little end table between. In the indent where the bookcases are now, you could put your taller curio (looks like crome colored) with a large artificial tree/plant. And I agree, a rug in front of the bookcases and in the couch area would tie everything together.

Wow, so many great tips! Thank you so much!

I've decided to buy another armchair to pair with that one and to put a big art piece on that blank wall (I do have a beautiful one in black-white-blueish tones, just need to frame it), as well as putting a nice credenza on the back of the sofa. Do you think that's enough for filling the space?

Regarding the rugs, do you guys suggest any particular style/color? I was thinking of a light grey one for the seating area...