Just leveling up to 85 and staying there, I guess you won't get so annoyed perhaps. But are you like me you'll sometimes be frustrated. I'm an altoholic having many chars from 20+ up to 85 and it annoys me extremely e.g. whenever higher level chars want to help my lowbies.

Two or more players located at the same place at the same time should always be able to see the same things! Now when zones changes depending on if you've done certain quests or not is just plain stupid if you ask me. You can't even see certain npcs until you completed certain quests.
Regardless of boxing or playing solo it really destroys the impression of this being one massive world for everyone to share.

This is my opinion and I do hope future expansion will not have any more open world phasings. (Phasing is only okay in certain circumstances like e.g. DK starting zone).