I've been putting off my thoughts on Amazing Spider-Man #512 for a little while now so the shock would were off.
I'm going to be brief and to the point. I think it's a good story (albeit somewhat hard to swallow logistically).
I also think it's one of the most thoroughly un-enjoyable stories I've read in a long time.
Let make myself clear on this. I've noticed a lot of people equate the words "good" with "enjoyable" but well they're completely different qualities in my own opinion. The Passion of the Christ, Schindler's List for instance are excellent movies, but the typical viewer experiences them as opposed to "enjoying" them. Likewise recently I "enjoyed" Paparazzi, a hilariously ineptly written and ill-conceived movie.
I noticed this summer we've seen not only a lot of bad happening to superheroes, but we've also seen some heroic characters doing bad things. Spoiler accidentally causing the mob war in the current War Games storyline in the Batman titles, Omni-Man in Invincible cold-bloodedly slaughtering the Guardians of the Globe, Alex in Runaways double-crossing his teammates, and the Justice League in Identity Crisis mind-wiping villains to protect their families.
To be honest, I think a lot of how your react to the book depends on your opinion of Gwen Stacy as a character. To be perfectly frank, when I was just getting into Spider-Man comics the only thing I knew about the character was that she was Spider-Man's girlfriend, and that she died. As I grew older, looking over those Black & White "Essential Spider-Man" collections and other trades, well... she struck me as one of those "plot girlfriends." Characters that exist only to get kidnapped, or get mad at the hero because he's late for a date. (Dana from Batman Beyond comes to mind as a recent example of this phenomenon.) And to I'd be lying if I didn't say Gwen was on my list of characters who became much more popular solely because they died. (See the Pre-Crisis Supergirl, or Aeris from Final Fantasy VII.)
Not that I'm saying there aren't good stories that can be told about Gwen, it's just well... in the state she was in when Gerry Conway killed her, there wasn't much to the character. True, the death of her father added bit of dramatic tension to the mix, but well... to be honest she's still not as interesting as Mary Jane or even Betty Brant. A writer wanting tell a compelling story about her would best be advised to try and add some layers to her character. That's what JMS tried to do. To be perfectly frank I'm not sure he went through the most well conceived manner of doing that.
What I find most frustrating about the fan reaction to book is a lot of them seem to be completely missing the point of the story, raising complaints of "he made Gwen Stacy a slut." When I think the obvious intention wasn't to so much sully Gwen Stacy, as make Norman an even more amoral. I mean the guy essentially took advantage in every possible way of a girl half his age in every conceivable way and then killed her the moment it became convenient. Gwen's no longer a saint, but she's still a victim in all this.
Perhaps what bothers me the most about the revelation from Sin's Past isn't so much the revelation as the timing of it. This summer to be quite honest, I've simply had enough shocks for a lifetime. From seeing Sue Dibny murdered (and sexually assaulted in a flashback), to seeing the X-Statics gunned down , and watched Mark's father in Invincible reveal himself as an inhuman murderer. I've watched one of the Runaways die a fiery death, seen Mia from Green Arrow being forced to take a man's life, witnessed one of Tim Drake's classmates get gunned down in Robin and watched this generation's incarnation of Gwen Stacy die in Ultimate Spider-Man. All this, and I haven't even gotten around to reading Avengers disassembled. Enough! I say... Enough already!
I'm sick of seeing all of this death and abuse, and suffering induced on characters I deeply like. It's just too much. And heck... even during the dark days of the Clone Saga and Heroes Reborn I could rely on a title like Impulse for some good light reading and well now that book is gone. The current Johns Teen Titans is an good read, I could have lived a very long and happy life without seeing Bart Allen was gruesomely shot in the knee, and Rose Wilson plucking her own eye out.
As much as it's easy to blame this current situation on writers and editors, the sad truth is the current state of the market is by in large a reflection of what the fans buy. Geoff Johns who writes the current Teen Titans book once wrote Stars & S.T.R.I.P.E, one of the best lighthearted child friendly books to ever hit the market. That book's now gone. Why? Because it didn't sell. Likewise the same can be said about Sentinel , Guardians, and some other perfectly enjoyable books. Why is Mary Jane being put on hiatus despite being one of the best-reviewed books put out this year? Because it's not selling.
And why are we seeing so many variations of the "in this issue an Avenger dies," or "Character X has horrible secret" sales pitch.
Because that sells.
And if you got a problem about that, don't complain, start voting with your dollars. Don't boycott stuff, start supporting the kind of books you want to see on the market.
Oh and would it kill you to give Mary Jane a try?