When I was young and an avid comic reader, this would have sent seismic shockwaves throughout the comic world. Today it's a shrug. After all, it's not really Spiderman since it's an alternate universe character. I'm told one of the Fantastic Four is in the crosshairs soon. Again, shrug.
Why the ambivalence? Because let's face it, they've killed Superman, Batman, Green Lantern, Captain America, Phoenix and every other X-Man at least once. They've all returned in preplanned fashion leaving the reader feeling used and duped. Believe me when I say nerds and geeks have long memories when it comes to science fiction abuse.
Case in point: The first comic I ever read was Captain Marvel; no not the Big Red Cheese aka "Shazam" but the Marvel Comics version. With all respect to Green Lantern, the Kree Captain Mar-Vell was my first and ever my favorite comic character. I followed his exploits faithfully each month... until they killed him. And they did so brilliantly. Not with an explosion, not sacrificing himself for the sake of the universe but facing his own mortality in the form of cancer. Each page was human, touching, heartbreaking and inspiring. Decades later it's still my personal gold standard of great writing and the journey following a character's arc to completion. It's the only comic I've still kept.
In the television medium, Buffy the Vampire Slayer's Joss Whedon is a master at character death; he gets it. Cultivating an attachment for a character takes time; both the writer and viewer have to have to find something in that creation that speaks to them on a personal level. Once that attachment is formed, then you can move to the next step. Watch the Buffy episode "the Body." Drawing from his own experiences, Whedon manipulates every emotion and meticulously crushes the viewer with the loss of Joyce Summers. We the viewers cared about the character and actually mourn her loss.
Stargate SG-1 has similar flashes of greatness in the episode "Heroes" where Dr. Frasier is killed. It rocked the series and changed the course of the franchise. Stargate Atlantis followed suit with a touching and meaningful demise of Dr. Beckett. Both were established characters embraced by fans and ultimately their ends were for effect. While both Dr.'s came back for singular appearances, the episodes were more or less for the fans to say goodbye. Well done. (Although it makes one wonder if Stargate physicians aren't the Red Shirts of the series)
As much as I love Star Trek, the writers have irritated me to no end with throwaway fatalities such as Trip, Data and to some extent Spock. (While both Data and Spock died in spectacular fashions, memory transfers lessened the impact and thus the meaning. I'll forgive Spock somewhat; lizard poisons Spock, after all.) Trip however will remain a source of being "cheesed off". Forever.
A character's death should be a gut punch; it should leave the viewer feeling breathless with a sense of genuine loss, not wondering how the writers will bring the character back. As a writer if you end a character to sell a few extra issues or increase viewership for a week, you've not only done the series a disservice but the fans as well.
We're your audience. Treat us with respect... and we'll keep coming back for more.