Yeah, like Boom says, "Nevermind" was a milepost kind of album, and there haven't been very many of those. "Sgt Peppers" signaled what was possible with modern recording gear. Van Halen's first record featured a new level of guitar virtuosity, and ushered in 13 years of spandex and hairspray (In the words of Bill Burr, "When I was a kid, you dressed like a girl and sang about the devil. Now *that* was music.").
The hair metal that VH inspired was the dominant sub-genre of rock music right up until the opening chords of "Teen Spirit." Immediately, the hairspray and the spandex -- all of it was over. The sound, the clothes, the haircuts, the cities that represented the cutting-edge ethos -- everything changed overnight. "Nevermind" did that.
I would add Van Halen's debut to Boom's list of albums that changed the course of musical history.
My own .02 as an aside here: Just like VH brought on a parade of terrible imitators (Warrant, Poison, etc), "Nevermind" brought on a parade of no-talent copycats with way too many layered dirty guitars (Creed, Nickelback). Ugh.
Anyway, "In Utero" was hugely anticipated as a follow-up, but the band didn't want to make Nevermind 2. Instead, they worked with a different producer/engineer (Steve Albini), whose sound was far less polished. I think the fact that the band pushed back against the label and chose to take a more low-fi, DIY path... it still inspires a lot of rock fans to proclaim it as the band's best work.
Personally, I think the songs on "In Utero" take a big step back, and I'm not wild about the Albini sound.