Just to start off we haven't done terribly too much to our living room space. It's mostly just been painting and redecorating but I think it just goes to show you what a transformation simple paint and a change of furniture can accomplish.
When we moved in the living room was like a cave. The walls were a drab green color and the windows were covered with blackout valances that never moved. When we toured the home it was so dark I couldn't imagine spending most of my time in there. It didn't help that the previous owners had also blocked the remaining window light with a television! It also wasn't very family friendly. I couldn't imagine all six of us trying to sit and watch a movie comfortably in that space.
All we've done is paint the wall a light minty color and the mantle white. But that ALONE was enough to transform the space. Decor-wise we opened up the windows adding only bright colored translucent curtains and changed out the ceiling fan (see that post here). We also added light colored furniture. There's still a lot that I'd like to do to the space (especially the mantle) but at least for now it's a place where I can work with lots of light and it's a space where we can all gather as a family and relax.