Def Leppard’s Pyromania wasn’t a drastic change in direction or musicianship from their first two albums, but the production quality went through the roof and truly set a new bar for heavy-metal-based pop in the 80s.
Oh, Jesus, that sounds like something Patrick Bateman would have said.
Alice Cooper – Welcome to my Nightmare
I never got the hatred for Van Hagar. Sammy was a better singer than David Lee Roth by most measures, gave them a #3 chart success with Why Can’t This Be Love and the song Dreams, while not as big a hit, has proven to have tremendous longevity.
I wouldn’t go so far as to say I hated Van Hagar, but it was just not the same band. Gone were Runnin’ With the Devil and Hot for Teacher, traded in for, let’s face it, pop rock. Van Halen I was just about the heaviest thing most people had ever heard at the time. Listen to that and 5150 back-to-back.
When Faith No More replaced singer Chuck Moseley with Mike Patton, the band’s sales took off with a #1 song (“Epic”) and several other hits off their next two albums.
Love: Forever Changes.
Not to mention their breathtakingly successful experiment with releasing that album for free online and only later (after hooking up with a new record label) releasing it in the conventional ways - and watching it sell over 500,000 copies. Their previous label, after a management change there, dropped them because - among other cited reasons - it was thought the album might only sell 100,000 copies.
Ted Nugent with the Amboy Dukes certainly had some success with Journey to the Center of the Mind and Great White Buffalo but, of course, everything changed when he came out with Stranglehold.
lieu, old friend, I am having trouble balancing out “Ted Nugent <> Artistic Breakthrough”? 
(I grew up on the Nuge and can still lay down a greasy version of Stranglehold thankyouverymuch…)
Bob Seger’s Night Moves. A unique, complex tune that shot him into stardom after years as a kind of rock journeyman
Ricky Nelson was a washed-up teen idol before “Garden Party”. After, he was a (somewhat grudgingly) respected elder statesman of country-rock. I think that qualifies.
If any band has, it would be the Stones. I’d say they tried with “Their Satanic Majesties Request” and failed, only to regroup and score with the real thing on “Beggars Banquet”. As Keith said, “a spell in prison will certainly give you room for thought.”
Maybe it’s just because I never got into Zeppelin all that much beyond being familiar with their hits, but I’ve honestly never been able to hear the similarity, though I’ve heard it mentioned many times.
The interesting thing about 2112 was something I recall Lifeson or Lee saying in an interview, that despite Caress of Steel’s poor performance, they couldn’t have made 2112 without having made CoS first. The whole Fountain of Lamneth suite on side 2 of CoS was sort of an experimental “proof of concept” (if only proving to themselves that they could do it) for the idea of a ~20-minute song that could be broken down into individual sections that would each stand on their own as a shorter song and still make sense.
The fascinating thing about The Fountain of Lamneth, to me, is that I completely didn’t get it when I first heard it at age 14-15. It was, as far as I could tell, an interesting if somewhat murky fantasy story. And in fact, I still didn’t get it when I was 22-23, the same age the guys in the band were when they wrote it. It wasn’t until I went back and re-read the lyrics after I turned 40 that it really hit me — the suite simply describes the course of a man’s life from birth to death (infancy, childhood, adolescence, young adulthood, marriage, middle age, dotage, and finally death), touching on the various important stages in that life, but cleverly wrapped up as an allegorical fantasy. I personally think it’s brilliant, especially considering Neil Peart’s age when he wrote it.
But the thing that made the album sell poorly, I think, was that it went over the head of the target audience (teenagers and 20-somethings). That, and corny fantasy cover art and an album title that didn’t make much sense had no obvious connection with the songs on the album. So with 2112, Peart wrote a more straightforward story in plainer language, and they included on the lyric sheet helpful written story text between the sung sections that made for smooth story segues between the different sections to make it more clear what was happening in the story.
On top of that, the album kicks off with the cool, swirly synth effects, and it got people’s attention. Musically, much the same thing happened a few years later with their Moving Pictures album, which to this day is still their most successful, most widely-known work. The leadoff song, Tom Sawyer, starts off with that now-instantly-recognizable descending synth effect that just grabbed people’s attention right from the get-go.
Now, from this musician’s perspective, IMHO The Fountain of Lamneth (TFoL) from CoS is more satisfying, musically, than 2112. As a bassist who was inspired by Geddy Lee to pick up the bass in the first place, TFoL, and in fact most of the songs on that album, is much more challenging and fun to play than 2112. 2112 is actually extremely repetitious and surprisingly simple compared to the overwhelming majority of Rush’s other work, before and since. But it may have been that relative simplicity that made it more accessible to the general rock audience. Then, once 2112 had swelled their fan base, those fans were now more open to checking out (and understanding) their earlier material, and were eager to hear the new material on the following albums. And that allowed the band to dive right back into the complex music and deeper subject matter of A Farewell to Kings and Hemispheres without losing their whole fan base.
Don’t get to geek out about Rush that often eh, Mister Rik? 
You gotta admit he articulates the case for 2112 being Rush’s BR pretty fucking well tho.
Led Zeppelin’s “IV” album, notably “Stairway to Heaven”
BeeGees “Saturday Night Fever” soundtrack, notably *Stayin’ Alive *
Michael Jackson’s “Thriller” album, notably Beat It (along with the video)
I might put Michael Jackson’s BR moment a little earlier, with Off the Wall. Thriller made him a megastar, but Off the Wall proved he was much more than just a former child performer and got him his first post-puberty Grammy.
Indeed - no disrespect MR; I love a good geek-out as much as the next…geek.
There’s also a strong case for Moving Pictures - four of that album’s seven songs have been concert mainstays/fan favorites for three decades.
No disrespect detected 
“Eat It” was at least as much Weird Al Yankovic’s BR moment as “Beat It” was Michael Jackson’s.