Along with Britney's omnipresent debut �Baby One More Time, Millennium's colossal sales sent a message clear and true: Teen pop was king, and it wasn't going anywhere� for another few years. It raised the stakes for teen pop's late 90s/early 2000s Golden Era. It's hard to imagine the likes of *NSNYC, LFO, BBMak and 98 Degrees hitting their heights without this record setting the example. Before Millennium, boy bands were an easy punchline. After Millennium, they reigned as pop tyrants.

Millennium served an important function in its time. Whether it holds up as an album 15 years later is a trickier question. Was it the best teen pop album of its era? No, I'd give that honor to M2M's seriously overlooked The Big Room. Was it even the best Backstreet Boys album? No, I'd put 2009′s glamorous This Is Us and even 2005′s derided comeback Never Gone a few notches ahead in the quality department. Millennium's sales record wouldn't even last that long - *NSYNC's sexified No Strings Attached would more than double its first-week sales only a year later, making our poor Boys look like also-rans in its wake. Millennium's success was less the beginning of a glorious run and more the beginning of the end - the Backstreets would release only one more studio record during teen pop's golden era before going on a five-year retreat, never again replicating Millennium's glories.

But none of this matters because Millennium, unlike many other "better" albums, represents the Glory of the Moment, exemplifying optimistic pre-Bush pop the way few other records do. It's the Backstreet Boys' one unqualified triumph, the sound of five handsome men storming the shores of teenage adoration and taking no prisoners. It's a record so in-the-moment, so immediate and so huge it was impossible for any pop-starved millennial teen not to get swept away by its power.

It doesn't hurt that the record starts with two of Backstreet's biggest and best moments. "Larger Than Life" is about the ballsiest boy band opening cut I can imagine. It's less a good-hearted fan tribute and more a public rally for their newly conquered Backstreet Nation. A.J. cackles like a madman, the verse explodes into the biggest chorus of their career, and there's even a shreddin' guitar solo. On a boy band record! Never had a boy band revelled in modern excess quite like this.

But "Larger Than Life" wasn't the first single from Millennium. It was no world-conquering anthem, but rather a victory dance for the war they'd already won. The song that won it for them? Millennium's first single and second track "I Want It That Way," one of the finest pop songs of its era and the only time Backstreet would strike the Universal Chord. "Undeniable" is the word. Not only was it a huge career-defining hit, but it won the hearts of teenage fans and thirtysomething critics in equal measure. It's the one Backstreet song you'll find on "Best Pop Songs Ever" lists, the one that'll make even the most rigid teen pop hater sigh and snarl and say "Ehh, okay, that one's pretty good." To hear it once is to understand immediately: its hooks simple, its delivery impeccable, its music video iconic.