Since it's late, I'll toss out a few for now. 
Heroic Opportunities. I think within a month people were giving up on them and tossing them off their hot bars.
There being 5-7 instances running by about the 2nd week of the game when everyone hit Antonica level.
Refugee island. I miss the boat start.
I remember that access quest to Enchanted lands too. Soloers and duoers really got upset they were knocked out of content unless they grouped, and were pretty vocal on the forums about it!
The game wasn't solo friendly. Majority of mobs were pack linked and/or at least ^, ^^, and ^^^!
Provisioner was the only craft not reliable on another crafter.