It's odd to dream of being young Tom Riddle surrounded by his Slytherin bootlickers, only to wake up to the body of Harry Potter, the Gryffindor, with his very Gryffindor friends.
It's odd to remember spells he doesn't like recall learning, sitting in lectures and feel like he's listening to them for the second time.
Except for Defence. Professor Merrythought was long retired and Harry has had three defence teachers in three years. It's variety. It also create unpredictability that Harry isn't particularly fond of.
Quirrell was possessed, Lockhart was a fraud and Lupin… He's too friendly and too eager to get close to Harry for no discernible reason. At least he's a decent teacher; it's the only reason Harry hopes he won't have to kill him. It would not be good if they had to get yet another teacher.