It's really great hearing this from you, got my hopes up that maybe you guys actually ARE trying to make this game what it should be and notice that it lacks a lot :)
I believe the Legendary buff, if done right, will be very good for endgame. Make high-end legendaries a bit rarer, and a LOT better, better than *almost* all rares, and you've got items to remember the game by.
Also I think a bit more complexity to hirelings, more gearing options and buffing them to make them similarly useful to D2 hirelings would help. Then, while gearing ourselves, we'd also actually have a good reason to waste money, time and effort into gearing hirelings.
Obviously new content is also needed, but I do believe these would also help.