Been there twice.
It's weird. First off, like most newer stadiums, the atmosphere is not what it was at old Yankee Stadium. The place is massive...sort of hard to believe that it only holds approximately 50K. When you're inside you'll swear it has to old more. Second, the seats between the bases are so incredibly overpriced that they're often empty...they've even been empty during playoff games. Weird vibe being in a mostly full stadium with all of the empty seats exactly where you'd expect them to be full.
Of course, this was several years ago when everything was "normal" in regards to attendance.