I have been cautiously optimistic about The Taken King since its reveal, but I'm probably going to be signing off as well (due only in part to this update).
First of all, I don't find much fault in any of these changes except for the Hand Cannon hip fire and magazine change. (Well, Icebreaker's change is pointless, but it's been obsolete for a while.) I definitely think the exotic Hand Cannons needed nerfing, but a global magazine size on top of that is too much. It didn't make sense for Hand Cannons to have an unusual amount of rounds in their chamber like 4, 5 or 7 to begin with. They should pick a number for each archetype and stick with it.
Like another poster said, I don't like using anything else in PvP. I've largely moved over to a Scout Rifle/Shotgun combo for PvE content, but nothing in the game lets you fight as freely and mobile as a Hand Cannon in PvP (The Last Word in particular). Without that freedom, the game loses vertical depth in favor of spray weapons like Pulse Rifles and Auto Rifles. Staying on the ground means being more susceptible to grenades, supers, rockets and people with the spray weapons. That was fine in the beta, but everything now is too lethal - especially at the high levels - to play otherwise. I was saying as far back as the alpha that the game needed a stronger focus on hip firing and vertical gameplay, and now they have naively gone and nerfed the little it had.
It stings especially because it looks like they will even be tuning class stuff like Blink. I've long waited for the day it'd be balanced, and that along with some of the new stuff I've seen like the Bannerfall map have had me very excited about the future as far as Destiny's gameplay goes. It looked like they had finally began to channel their Halo roots.
Again, most of these are good changes, but the one that appears to hit hardest comes at a time when the last thing I need out of this game is bad news. I'm literally signing off anyway because my PSN account has been suspended for disputing a charge. Sony wants me to spend a ridiculous amount of money just to have access to my account again. There is no way that I am throwing money down the drain like that.
I'm not going to deny that Destiny had me hooked. It's a flawed game for sure, but it was a blast to play with friends and simply fun to shoot stuff in even when there was nothing left to do. That alone has made it more interesting to me for a longer period than any other game I've played - including Bungie's previous games. Nevertheless, I've reached a point where I've had enough of the bullshit, whether it's in the game or out of it. Between all of the controversy and the mismanagement of the game itself, being a fan of Destiny isn't worthwhile anymore.