I think open spaces are a great thing. It bugs me when maps are littered with tons of unnecessary and clearly artifically placed cover -- Brothers in Arms comes to mind for sure.
Open spaces provide the attackers with unique challenges. When there is always cover spaced out every 20 feet, it definitely takes the fun out of it. It also kills the immersion when there is a pile of random crates or barrels standing out of place in the middle of nowhere ... it just looks wrong and plays boring!
I hate to say it, but this screen shot shows what I'm talking about:
I mean I guess it kind of makes sense in this industrial setting, but all of the cover still looks highly artificially placed, kind of like something in Brothers in Arms. It's too bad, too because the map otherwise looks unbelievable. All of the crates and barrels are at perfect geometric angles that just happen to provide people with the perfect cover ... it just makes an otherwise realistic looking scene look very strange.