the biggest new thing is going to be that you can play as different races, like the charr.
and, they're cleaning up the gameplay so that you can do a ton of new stuff, supposedly, maybe including jumping and the like. they're definitely going to be adding a TON of new missions.
EDIT - if they raise the level 20 limit, i'm not playing anymore. how can it be a true corpg if they let you level up to 100 or something ridiculous?