I love right clicking to put items into or out of my stash.
I love clicking on a banner to go straight to the action in a public game.
I love the concept of dyes for armour (my character looked like a jester before dyes).
I love being able to see another players gear and skills with a mouse click.
I love playing around in the Auction House.
I love, love, love not having advertising filling my screen every 30 seconds, making it unplayable.
I'm sure there are lots more, but these spring to mind. What are your thoughts.