I've run most of the new instances in the beta on heroic, and they're not that bad. I think there's a lot of talk about everything being rough and tough and requiring CC, but I just haven't seen it in practice.

However, there are some very annoying new mechanics that are going to be a challenge to overcome. A few of the bosses in HOO require some large group movement and several different mobs to be targeted by different people at the same time, and the mobs all have the same name, so it could really get interesting.