An impressive metric, and the landscapes seen in the videos to date have been stunning (I could lose myself in just being immersed in such a detail-oriented game world), but a big part of what makes such a large area fun to play is by the developers packing in things to do, see, explore and participate in. To me, little would be more boring than exploring large, wide open areas, with there being no discernible interaction for as far as you could see.
If these lands are as large as what has been speculated, I'm hoping the good folks at CDPR have us lined up with a good amount of non-repetitious "to do's". I can easily see this game taking 150+ hours, because I am going to take my time from the beginning. Hopefully there will be a certain amount of side quests you can do without even having to progress the main quest. That truly gives me a sense of freedom.