You are fortunate that your fiance has good taste in furniture; it could be so much worse! And he has some sense of proportion and has picked some good pieces.

That said, there are several things you can do.
1. Area rug in living room. It will anchor that seating area and give you an opportunity for pattern and color,depending on your choices. First, you're going to have to agree on what color you want to use a as a focus. Most men will pick red or blue, but you might explore other options: rust, ochre (an earthy shade of yellow), turquoise, patterned B/W. Depends on what "vibe" you want to project: sophisticated, homey, traditional, etc.

2. Curtains. Personally, I hate blinds, but you may have no problem with them, and you may need these for light/heat control. Even if you keep them, hang curtains that can be drawn over them or flank the windows. These can be silvery gray shantung (a particular weave of silk done in lots of faux silk draperies so it doesn't need to be pricey), something with a pattern in white and gray or white and whatever color you choose. You want to coordinate this with the rug, which you should probably buy first as it's going to be a game changer.

3. Art. What's there is hung too high (6-8" above back of sofa), but you could replace both pieces with something with color once you decide. Don't distress if you can't find the perfect thing right away. Meanwhile, hang these 2 pieces elsewhere and leave the wall bare to motivate you, or hang them one above the other. Staggered like that is dated.

4. Pillows and throws. A colorful throw over one of those leather chairs (great chairs but the whole thing is cold) and a couple (only 2) colorful pillows on the sofa.

5. More lighting. To the left of that sofa (from the perspective of the photo above), a floor lamp. Perhaps one of those arc lights? There are tons of options.

Bedroom in a separate post.

Bedroom: This is an intensely masculine apartment so you have some work to do. Again, curtains to soften. Plain white would work, but a pattern would add some interesting contrast..

Change the bedding. A throw across the end (for afternoon naps), change the decorative cushions to something lighter (patterned w/b or w/gray, gray/color -- the choices are endless), and some light-colored sheets (pale gray?)

The mirrors don't quite work. Another option for colorful art.

Taller lamps. It's hard to tell just how tall these are, but they look short. Perhaps something in mercury glass or another metallic finish for some reflective quality.

Although most people don't bother if they have carpet, you can put a rug under the bed that goes from side to side. It has to be a larger one (5x8) as you want at least 2 ft on either side and some showing on the end, too. Another opportunity for pattern and color that could lighten the overall atmosphere.

The color pallette is sophisticated and sleek, uncluttered, which I can appreciate. If your fiance pulled this together himself, without the assistance of a decorator (or his mother), then he has good taste and very specific taste. He may be resistant to change. You might want to find this out sooner than later. Good luck! And happy decorating!

Here are a few examples -- not to suggest color, but how your rooms might change. Search houzz. It's a tremendous resource. Go through every magazine you can find. If painting the walls are an option, it can make a huge change. Test before you commit.

Hi angeliquee29, i would put an area rug to make that space feel warm, and like it is a seperate space to the rest of the big room. here are a few pics with black couches so you can see how you feel and what colours you like... let me know what you think :)

Thank you for your comments. I definitely think both spaces need colour. My biggest issue in the living room is the fact that the entire wall behind the tv unit is simply a brick wall which also makes the apartment look unfinished.

Everything is just brown. Everywhere i look its brown. Couches, chairs, tv unit, bedroom suite.

Your brick wall is gorgeous but too much of a good thing ! I would cover part of it - how about a tall wide media -bookcase, in black

Definitely a rug to warm up the place

I would add bright throw pillows and a great rug to pull the room together it would give it the pizzaz you are looking for.

Thank you everyone. Think i will start with a rug and a few cushions in a colour we agree on-perhaps a yellow or turquoise. I tried a cream throw over one of the chairs as it was something i had already and it already makes a difference.