Better Distinctions Between Classes
If the three classes of Guardian in Destiny are each meant to have their own set of strengths and weaknesses that correspond to an archetypal D&D class, such as the paladin (Titan), ranger (Hunter), or wizard (Warlock), then the sequel ought to be far more committed to the idea.
As it stands, I can't tell you how many conversations I've overheard in which MMO veterans or RPG die-hards with years of gaming experience can't agree on what, precisely, the Guardian classes – and their subclasses – are meant to represent. Is the Warlock a cleric? People have suggested as much, but then why can they only resurrect themselves? It's not as if they go around healing the wounded. They do, however, wield the kind of space magic befitting a mage or wizard. Titans are all about protection – safeguarding the Last City against the Darkness and its minions – so what are we to make of the Striker and Sunbreaker subclasses? The Hunter's gunslinger-style mix of speed and stealth is vague enough to apply to all three of its subclasses, but that's an issue all its own.