It's too early to know exactly what influence George R. R. Martin's A Song of Ice and Fire will have on the fantasy genre, though it's a safe bet that it will be significant. But it's pretty obvious that the Red Wedding scene all by itself will have a significant impact -- and a good one, too.
One of the signature weaknesses of a new writer is a tendency to be too nice to one's characters. Some weaknesses, such as a propensity to spend five to ten pages of a story "setting the scene" before finally getting around to the plot, can be cured simply by clearly explaining why they're a bad idea and how they can be circumvented. But when all of one's upbringing is devoted into turning one into a decent person, it can be hard to undo. "Look, I'll say to my students, on those occasions when I teach. "It would be a heinous act to throw a woman into the path of an oncoming train. But we celebrate Tolstoy for doing so in Anna Karenina. These are not real people we're dealing with here. They're only words on paper. Make those bastards suffer!"
They hear but, half in love with their own creations, they do not easily believe.
There's a lot to admire about the Red Wedding, including the fact that it took the readers and later viewers by surprise. I'm sure there are many new writers out there at this very moment feverishly plotting out their own massacres in imitation. And that's good, because while most of those bloodlettings are destined for the drawer, they're a positive step toward publication. Many more writers are taking to heart George's exemplary willingness to kill off characters who've won the readers' affections. That's also good. But the chief lesson to be learned hers is to let your darlings suffer.
Why is this desirable? Because there are things we must learn in life which can only be learned through suffering. If that suffering is experienced only in our imaginations, so much the better.
Also, it can be wonderfully entertaining.
The opening of the Honest Trailers spoof of Game of Thrones begins "From fiction's most notorious serial killer..." But let's be honest here. It should be "From fiction's most beloved serial killer..." I trust that any new writers reading this are taking the implicit moral to heart.