I'd like to say that I actually really enjoy playing Destiny. I played through the whole game with my friends, and it was and still is a blast. That being said, there are a lot of disappointing aspects to Destiny as well. Here are some of the things that I think Destiny could have done in order to be a better game. Feel free to add your own points as well and lets see if there truly are 100+ things about Destiny that could be improved.
1. Destiny feels like it has a rich world, filled with many characters and lore. But the delivery mechanism of this story is mostly through the Ghost, who vaguely explains some details to the player, while they are loading into a new level. It's too much talk and not enough show. This is an easy remedy; stick to the tried and true formula of using cutscenes. If Destiny showed us some of the stuff that it talked about instead of just talking about it, there would be a far greater sense of world instilled in the player. The few cutscenes that Destiny does have are easily some of the best story moments in the game. More Queen anyone?
2. The amount of loot that drops from enemies is really disappointing. You could farm for hours post level 20 and still be rolling around with green or blue gear. Even playing through the Crucible doesn't give enough gear. The amount of loot dropping should be significantly increased, even if most it is garbage. That way even if you do get garbage drops, you can still dismantle them and get useful parts for crafting.
3. You should be able to get weapons in more ways then just getting loot or buying them from vendors. If Bungie doesn't want to increase the weapon drops in the game, they should at least have different crafting components drop, which can then be traded in for actual weapons. I'm not talking trading in some random Spinmetal and getting marks and then getting weapons. I'm talking actual variety in weapon parts.
4. As an extension to crafting, players should be able to customize weapons. Instead of having the same gun drop over and over again with some slight difference to stats that barely amount to anything, players should be able to use weapon parts that they find as drops in the game to customize their weapons. New sights, new silencers, new alt fire options, new modifiers, new skins, new everything. It should be customizable in such a way that even if two people have the same base gun, what they have done to it through customization would make them act wildly different. Those same ideas should be applied to armor; instead of having armor with preset modifiers that randomly drop, the player should be able to min max how they want their character to feel and look. Individual gear shaders would be cool too.
5. There are times when you as a player just seem to be having terrible luck, but your friend is getting a bunch of loot that he or she doesn't want. You should be able to trade loot with your buddies in order to help each other out. You moving on to Exotic gear? How about passing on your old Legendary why don't ya?
These are a few of the things that I've been thinking about on how to make Destiny a better game. There are probably tons more that I'm not even thinking of at this moment.