I saw them last night as well. I'm not sure the towers/arrays do a great job of dispersing the high end. We couldn't hear any guitars during Mammoth or Pantera, or maybe just a hint during the solos, if you focused. Otherwise, just a lot of muddy low end, bass and drums, and some vocals buried in it. I got up a couple times to check out the merch line, and once to hit the restroom, and it seemed like that in other areas/levels as well. By the time Metallica took the stage, they'd dialed back on the low end considerably, and we could hear rhythm and lead guitars, and vocals.
I get that sound reinforcement in a stadium can be a challenge, but at their level they should be able to do better than that. I thought Metallica played a good set though, and nice to hear some of the older tunes, which tend to also be the solos I prefer.