Destiny is in a downward spiral due to these reasons:
1. The nightfalls are completely useless. This week i got 3 pieces of legendary gear all under 300...and they said they buffed rewards? Sorry, they didnt. All they did was replace antiquated runes with ghosts. What really kills nightfalls is the loss of the xp buff as well as the 500 reputation gain. This was the only reason some people still did nightfalls pre TTK if they already had all the exotics. There are no incentives anymore. And it really doesnt help that turning in motes of light is the only effective way of earning rep.
2. Raid drops are atrocious. A while ago i ran hard mode 3 weeks in a row on all three characters and the best thing i got was 312 gauntlets from oryx. This combined with the fact kings fall is very boring after a while, has led me to only do the raid once a week if that. All the friends i play with are the same, we just dont care about the raid anymore, its just not worth it.
3. Events like Trials and Iron Banner are the only reasons we still play. Last week was fun because everyone was grinding for that rank 5 package for a chance at a cool drop. However when i say "fun" i mean "well its worth it in the end." I usually like iron banner, but clash is atrocious (Snipers camping in their spawn with seemingly infinite special ammo all game). But overall it was something to do. I enjoy Trials, its fun, but the rewards from mercury are lackluster, all you get is one gun 310-320. And the guns just arent that good (aside from the auto rifle which is god tier). But in the end crucible events are fun and are probably the only reason i still play.
4. Half of the advertised content isnt in the game. All that exotic armor, all those shaders and ships, and a few more exotic guns. MOST of the exotic armor that was seen in TTK trailers is not in the game. And then all those cool ships and shaders in the kiosks, completely unobtainable.
Here is the main point, [u]Nobody cares about being 320 anymore because it's too much of a grind.[/u] In year 1, getting max level wasnt nearly as tedious and always felt more rewarding (yes i remember forever 29). And really whats the point of grinding to 320 if the next dlc (if there is one) is just going to negate all that progress anyway?
And think about a typical week in destiny when theres no trials or iron banner going on...pretty boring isnt it? The nightfall is garbage, the raid is boring and unrewarding, so really the only thing to do is play pvp which it seems half the player base doesnt like anyway.
Destiny is in the same position it was in between dark below and HoW, i personally stopped playing for 4 months when they delayed HoW. So we have challenge mode on the way now, but is it really enough to keep players?
Oh and im not even going to dive into the horrendousness that is Refer a Friend.