I definitely have a huge love/hate relationship with Destiny. It does so much so well, and tries to be forward thinking, but then ties it's own shoelaces together. So basically here's my wishlist.
If D2 wants to be on PC it can't have 6v6 multi with Peer2Peer Skill Based Matchmaking (P2P SBMM), it needs to use servers. The lag in multi after Taken King had dropped off a bit was insufferable.
Raid matchmaking needs some kind of help for those who don't have a ready made, or weekly group to play it with, some kind of sherpa system or a way to make it accessible.
More depth in the open world spaces.
Don't make it so a quest is (warp into tower) pick up quest (warp to planet) do quest (warp back to tower). I'm hoping that removing sb360 and ps3 increases the overheads Bungie has to work with in D2 and makes it a much more fluid experience.
Put the grimoire in the actual game ffs.