Well first, I love the big window and the wood floors! I had the same large space with no definition issue in my condo when I first moved in also. I would put a small dining room table by the corner near the kitchen with some bar stools behind it. I would also put a LARGE area rug by the window side to separate the living area from the kitchen. Putting a couch facing the window in the middle would also create a good divider between the two areas. Maybe some small chairs facing the wall you plan to put the TV on as well. While I like the idea of adding a piece of drywall over the fireplace, I personally would be way too lazy to do that! Instead you could lean a large picture against the wall to give the illusion of a flat surface behind it? I guess it depends on how deep the corner is!

Thank you both !! Excellent ideas and I've printer them out as a reminder. Smart reminder to measure twice, buy once. I've made that mistake in the past.

Get ideas by typing "casual great room" in search box of HGTV.com. Put a small dining set at the right of the windows. Put a living room seating area in front of the fireplace and where you plan to put the tv. Be sure to create an intimate and close seating arrangement. Some people stick the seating at the back of the walls. That doesn't allow for conversation or a nice seating area. Define your living room and dining area with two separate rugs, as potchie recommends. Measure twice, buy once! Sofas can measure from 60 to 84 inches and beyond. Keep in mind that furniture looks smaller in a store than it will in your living room! I can't wait to see the results!

much depends on what you have to work with. invest in a piece of drywall to apply to the back of the FP, covering the deep corner....it will make the FP more substantial and will allow you hang a great piece of art there. a little wall color will have big effect and define the 2 areas with large, coordinating, but not matching area rugs, be sure to hang all curtain panels high and wide for good scale and use plenty of large scaled wall art...small pieces will end up looking cluttery in this big open space. create an L shape with the sofa/seating options...which will allow the tv and the FP to share the job of being focal point. you can soften the look of the back of the sofa with a console table, bookcase etc with a lamp. keep us posted with more pics and info!