Sound was not great his voice sounded good.
Yeah the venue is awful for big rock bands like U2. The stadium's acoustics were designed for football, so if the crowd's small the noise would still be loud and make it sound like a bigger crowd's there. Which makes it hard to soundcheck because crowds make it different. Also, the roof was open for the start of the show but was closed later (during the TJT set I think) due to a bit of rain (it was only a light spring shower, hardly anything!). So the sound was affected by the roof. I don't know if U2's techs did proper soundchecks, it could have been better. But honestly, it still sounded great for most areas (just a bit bass heavy).
Phone recording quality varies too!