Man, have you paid any attention to the forums? The number-one complaint, far and away, is cores for infusion. The number of hugely upvoted posts on getting rid of cores for infusion absolutely dwarfs any other topic or complaint. Just as ONE personal example, I have a friend — the guy who introduced me to Destiny, actually — who has straight-up quit until they make the PvE side of the game less of a bland, boring grind (mainly for cores.) And I have absolutely no doubt that he's not the only one.