Remember back in 2012 when we were all sorted into our houses? Everyone was either happy about being sorted into Gryffindor or commiserating about being sorted into Ravenclaw, Hufflepuff, or Slytherin.
It was all anybody could talk about around my college campus. People were dressing up as characters from the book. There was a girl who walked around in a Bellatrix costume for about a week.
I'll admit that being sorted into Hufflepuff was a giant blow to the back of the head the day that I took the quiz. Hufflepuff; the house that housed the likes of Cedric Diggory and his finders ("A Very Potter Musical" was big as well; start at 1:02, watch the full musical on youtube).
I eventually learned to accept that I was a Hufflepuff and that Cedric Diggory, ruined by his movie and musical portrayals, was actually pretty awesome.
As a side note: Peter Diggory was a British gynecologist who was a central member of the Abortion Law Reform Association and indispensable to the Abortion Act of 1967. Take that, Ravenclaws!
When Pottermore closed for renovations in 2015 and reopened a few weeks later, we were all disappointed to see that the sorting hat quiz had gone. Pottermore had promised to bring it back, but had given no indication of when that would be.
When the quiz finally did come back, I was sorted again into Hufflepuff. But the internet blew up with dissatisfaction with the new quiz. People who thought they were Hufflepuffs were Ravenclaws and Gryffindors were Slytherins and every permutation of the four houses.
Hufflepuff was no longer the house that no one wanted. Almost everybody wanted their old house back.
Most of the people complaining had been in another house before being sorted into Slytherin. I can understand the shock, but Slytherin has produced some truly great wizards.
Salazar Slytherin, perhaps the greatest of all Slytherins, was a teacher and founder of Hogwarts School of Witchcraft and Wizardry. Motives aside; he created an underground labyrinth that not even the Marauders could find.
Merlin was sorted into Slytherin and became one of the greatest and well-known wizards of all time. The Order of Merlin was named after him, and any one of his possessions is used to make some interesting swears (Merlin's pants, Melin's beard, Merlin's saggy left butt cheek, etc).
Horace Slughorn was a Slytherin, a teacher, and has no evil tendencies at all. He even called Lily Potter, a Gryffindor and a muggle-born, one of his favorite students. Remember the lily petal that Lily gave him (one of the best things ever to come out of the movies)? Remember how he couldn't bear to retell that story? Try telling me Slughorn was a bad guy.
Here is the thing about the whole Pottermore sorting ceremony. The houses do not define who someone is; what defines us are our choices. The houses simply provide a group of like minded individuals to board with.
Remember Dumbledore's words to Snape:
"Sometimes, I think we sort too soon."
Dumbledore is not talking about the sorting ceremony at Hogwarts; which are only assigned to allow for like minded individuals to board together. He is talking about the labels that we assign to people; good, bad, dumb, smart, etc.
Ever heard the saying, "Don't judge a book by it's cover"? Dumbledore is saying the same thing: Don't judge who a person is too early on, because people change.
Pottermore may have sorted you into Gryffindor in the past, but now you've been sorted into Slytherin. The quiz hasn't changed; you have. You are now more cunning and secretive than you previously were and Slytherin suits you better. Maybe you are more trustworthy than you were last year and you were sorted into Hufflepuff. Either way, you're now a deeper and more interesting person than you were yesterday.