I loved the evolution and iterative nature of Destiny and look forward to continuing that evolution/experience with Destiny 2 which is easily my most looked forward to game and will continue to be my most played game (3000+ hours in game [4000+ counting orbit/social spaces] across 4 characters on Xbox [one deleted] and 1 on PS4).
Destiny 2 looks like a bigger, grander, more refined experience at the outset with attention supposedly paid to/focused on Patrol Exploration and generally more stuff to do like Lost Sectors, Public Events, Heroic Activities, Adventures, and Side Missions in addition to the tried and true Strikes and Raid to go along with big changes to the PvP side of things and hopefully their best and most significant Story Campaign.
Edit: And that's not to say that I thought/think everything was great with Destiny throughout it's evolution up to this point as I've had complaints just like every other player but the overall experience is still second to none for me. It just means Bungie and any other developer isn't catering to just one player, group, or community and never will.
With that, I did think they might add more elemental properties to the game like (gasp) poison and ice while also adding a system in how the elementals react to one another and the environment while maybe adding another class and a totally new subclass for each existing class. However, if they can tweak and rebuild each existing subclass and make them as balanced and viable across as many game modes as possible I'm fine with that too.
My biggest complaints were always the patrol play-spaces and the activities or lack of that you could do in them so I'm really looking forward to the bigger and seemingly more varied play-spaces where we'll be experiencing stuff like Lost Sectors, Adventures, etc while they hopefully continue to add playlists and different ways to keep old/existing content fresh on a weekly basis through modifiers, difficulty, rewards, etc.