I've been playing D&D since '84. As a result, I'm one of those players who actively looks for opportunities to roleplay. Every character I make has some sort of mindset, and at least a trace of background (even if I don't bother filling out the bio). This is hindered in-game by two things.
First, the Say channel doesn't get enough use. I think there's an easy fix for this: include an option for floating chat bubbles, so that if you use the Say channel it shows up over your head, just like how NPCs work. This option already exists in LotRO, and I think it encourages people to say things in-character. Include the ability to change your chat input to the Say channel, so you don't have to try to remember to type /s each time.
Second, allow some interaction with elements of the environment. The biggest offender here is the taverns. Stormreach has these massive, sprawling bars with multiple levels, balconies, and out-of-the-way alcoves, with dozens of tables and chairs all around. And the only people who can actually sit in these chairs are the NPCs. The only reason people go into these bars is for the occasional quest, some PvP, or because they just died and recalled.
I suggest making the chairs in these bars targetable items (assuming that's a word), where the Use key makes your character go to it and sit down if it's unoccupied.