Mob positioning is the biggest change in roles that I've come across so far. As an Enchanter I have on many occasions used aggro to position mobs. There have been very few instances where I couldn't get aggro if I wanted it and couldn't lose it if I didn't. Sometimes staying alive in between can be tricky though, luckily I play with the best cleric in the game.
Being a pure caster I never have to be toe to toe or even facing mobs so I nearly always play in 3rd person. I started that back in Paludal caverns as a puller for a high dps group. I just stood in the middle and panned around to see all the mobs at the spawns, even the ones in the tents. Target, BCB, Slow, repeat.
Now as a melee... OMG! ....your target is out of reach... you cannot see your target... all the big melee push, caster push, pet push, make it stop make it STOP!
I catch myself moving backwards about 6 paces, then sitting. In most instances (if I'm doing my job) I already have the mobs attention so he will come to me. Luckily at 52 most mobs I encounter don't summon yet. If I don't have his attention, most likely I will now because I sit. Result = mob comes right to me and I can commence with the beating he deserves. Bonus result = pets and other melee are now BEHIND the mob pushing toward me instead of to the side. The downside, everyone else gets the out of reach, cannot see target messages. And if they happen to be afk or not paying close attention we lose their dps. Getting summoned changes this but most mobs have a recast of some sort to their summon. So if you act quickly after being summoned you can still get the mob to chase you to the point you want him.
Third person as a melee is much more difficult. I still prefer it but depending on where we are hunting, especially if I am pulling its hard to stay in. I usually toggle between 1 and 5.