Yeah for me there are two seperate things going on, and IMO it kind of fails both of them, but the second is much bigger a deal than the first.
The first is simply is the use of dynamics in a song effective. For me, a really quiet intro that, when the song kicks in, it doesn;t FEEL like things got louder and more intense, doesn’t really work… but that’s subjective and I definitely get not everyone is going to feel the same.
The second though is if you’re actively listening to something, on a good stereo system or on headphones, over time a really flat, squashed mix is physically tiring to listen to, because your ear isn’t used to hearing anything with no dynamic range. The first album I had this reaction to was RHCP’s Californication - I’d never loved the band but a buddy was really ito them and used to play that album a lot when we were working together, and i could never figure out why I actually liked a lot of the songs but there was just something viscerally offputting about the album for me that made it hard to listen to… until a decade lader reading an article about the “loudness wars” that waa flagged as an early offender.
But, also, some people just seem to be not very sensitive to that kind of stuff. I have a buddy who released a self-produced album that he absolutely brickwalled, and to this day new music he works on continues to be absolutely smashed (though he’s moved to doing more heavy-handed compression in the mix before he even moves on to mastering). He loves how it sounds, it’s very “modern” to his ears. It’s physically painful to mine.
I guess I’m just not that metal.