When I was a young kid still deep in my emo phase, Fall Out Boy were a major musical inspiration on From Under the Cork Tree, and seeing them explode was really a moment in which I became more interested in music more generally. For that reason, Infinity on High was an album that I still listened to an exceptional amount, but even then as a very young teenager I didn't quite find myself as engrossed in the groups sound compared to their breakout record. A little retrospect goes a long way on this one.
I think the easiest summation of the groups drop in quality is pretty brief: self-awareness. Where Fall Out Boy initially weren't going out of their way to impress anyone by changing their sound, Infinity on High sounds like it is directly trying to appeal to the massive audience they had officially been introduced to. The harder edges are deeply softened, and the grander production waters down the punk aspects of their sound, opting instead for unapologetic pop bangers. As derivative as the album is on the surface, it still excelled at its primary goal of maintaining momentum, and ultimately there are some really stellar sounding songs on here that still stick with you.
The most obvious drop in quality is Wentz's songwriting. Like, by far. His creativity and biting wit are so removed from Infinity on High that it's unmissable; the songs range from unimaginative one-liners to unrelatable jargon about their newfound fame. It's deeply cliched, and there are very few moments in which the songwriting doesn't force you to cringe at how tone-deaf the album is to what made the group so popular to begin with. Every song is guilty of this offense, and it brings down the quality of an otherwise at least catchy and fun record.
Infinity on High wasn't afraid to show its hand in many ways. The pop punk movement that had come into swing only a couple years prior was already emphatically on its way out, and Fall Out Boy drove the first nail in the coffin. Had Fall Out Boy maintained their previous sound it could have proved that pop punk was something worth investing in, but instead the band actively proclaimed that the only way to survive in a music scene is to adapt to what you think the people want. I rarely throw this term around because it's a pretty overused and misunderstood one - Fall Out Boy, deeply and truly, sold out. One has to wonder what could have happened to rock music had the group done something different here.
Favorite track: The Carpal Tunnel of Love