With your original pictures - I agree with larger rug. But I don't agree with comments suggesting the rooms are monochromatic. They are lively indeed. I think you are just missing some accessories! Art work on the empty walls - even just a single large dramatic piece is in order. In the bedroom on the white wall, in the living space behind the sofa, in the greenish bedroom behind the two beds. Those are instant areas where you can improve. But I think your spaces are lovely and well put together. Also I agree with the comment about table lamps - some of those would really add something, and your coffee table looks so empty - maybe just one gorgeous bowl, or stack some books. These rooms are 90% done in my opinions, just need a few finishing touches. Some of my rooms come out like this because the clients are not willing to pay for those last few finish items or feel they can do that part themselves...

I would fill in the hole........

First of all, I don't think that furniture is comfortable enough to sit and watch TV, so the TV should be remove from that room, the purple wall paper and the purple furniture is too much, you should consider another color for that wall and the furniture against the wall it doesn't look good. What is that room at the end is kind of dark and I cannot appreciate exactly what is the purpose of that room. I'm a firm believer in skylights, we have skylights in the laundry room, kitchen, living room and office, they make a big difference. (if you cannot have skylights (or tube lights) can lights are a great option. There are a lot of great ideas from everyone. I can't wait to see the after photos.

If you want some natural light you could run some transom windows across the top of the bedroom wall but there are lots of bathrooms that have no natural light and are lovely.