Harry also hits on an Asian chick, which I think is a neat direction for this franchise to take.
Harry Potter and the They're Not Even Trying To Make These Accessible to People Who Haven't Read the Books Anymore
What We See in the Trailer
This trailer is just a series of wand points and explosions. There's some mild exposition dropped in -- Principal Gandalf II has a problem that only Harry can solve, which shouldn't really be all that compelling anymore since it was established in every single other movie. Ron is in love with some chick we don't know and the Girl One hits Harry with a newspaper (which is a silly weapon for a wizard to use). But after that, ghosts fly around, Professor Alan Rickman shoots stuff, Kid Nazi stares in the mirror to pump himself up to do something aggressively Nazi-esque, one imagines, somebody screams "HARRY" and BOOM, more explosions.
What I Think It's About
There's something [blank] happening at Hogwarts, and it's up to fucking Harry to save the day. This is quite possibly the scariest and most evil [blank] to ever threaten the school, but Harry will rise to the challenge and learn that, in the end, [blank blank blank]. Professor Alan Rickman and Nazi McBitchface will inexplicably continue to live. Explosions.