Destiny's gameplay was extremely good in terms of running around and shooting things. Not knocking that aspect at all, but it could easily have met with WoW type success had their storyline/content plan been up to snuff. They changed the item system a bunch of times and never really met the expectations of what it could be in terms of the class / subclass system.
Activision has all the necessary pieces, they just did not make use of them at all well. Taken King was fun, but I couldn't muster any interest in myself or my gaming peeps for Rise of Iron,which honestly looks like the most generic excuse for "expansion content" ever. It's like if Mass Effect had released a Topeka Kansas expansion that focused entirely on fighting domestic terrorists.