Definitely go 3d. The special effects are spectacular. Especially the battle scenes of which there are many.
Don’t count on a quidditch match for a bathroom break, there isn’t one.
Deathly Hallows Part 2 can be enjoyed as a stand alone movie in case you have been holed up in a cave in Afghanistan for the last 10 years or so ago.
The dementors take on a more corporeal form in this film. I preferred when they were more ethereal, but it works well with the 3d.
For optimum enjoyment, see the last movie in preparation.
Hermione is always astonished to realize that Ron is not as dumb as a box of rocks.
Don’t play “got your nose” with Voldemort. It makes him angry. You won’t like him angry.