Harry's parents would probably still be alive and his school days would generally not include something impressive and dangerous happening at the end of the year (a bit like how Harry's son Albus had pretty boring school years in The Cursed Child).

Well, Harry would've had parents and grown up like a normal wizard, not be new to everything and he would've had a relatively normal run at Hogwarts (though what in Hogwarts is relatively normal?) Cedric Diggory would still be alive, as would Sirius, Remus, Nymphadora, Fred and Dumbledore. Bill wouldn't be a werewolf. And a lot of other things