I didn't like that all the Slytherins that got screen time were evil. Most of them were unlikable. And the few good Slytherins that were mentioned were mentioned in passing. I can't believe an entire house is just evil people so I can only assume JK Rowling just didn't care enough to show that the house is diverse.
I found both Sirius and Regulus interesting. Although Sirius wants to be different from his family, he's not quite as different as he'd like to think. For instance, his prank on Snape. He almost killed a classmate. He also gets enjoyment from humiliating others and pulls pranks on everyone, sometimes, like in Snape's case, cruel ones. Sirius can also be a hypocrite. Like when he tells Harry that you can judge others by how they treat those that are below them. Yet he treated the house-elf Kreacher like crap.
Yet Regulus who was supposedly the bad one (he was a Death Eater and all that jazz) treated Kreacher like his friend. I feel that the two could have stayed close if they had put effort into their relationship, but I think that Sirius probably refused to see his brother as anything more than a bad Slytherin an probably ignored him in favor of his friends like James. It's such a shame and it's sad that Regulus died so early.
"Yet Regulus who was supposedly the bad one." - Yes, it might look like that, but THINK of it; really THINK. I pretty much understand Sirius´ POV, but his brother could not have been evil. I always thought that he was very shy and very timid, but finally found courage to battle against things he could not bare any longer.
Imagine Regulus´ position and POV. Most of his life, he had been living in a lie due to evil "pure-blood" upbringing. Therefore he MUST have thought that Muggles are stupid and wizards are the good ones. It was LOGICAL for him. He never thought of fighting his mother´s opinion; he was meek and she loved him for it because he could be very easily manipulated.
Sirius, however, was different. Seeing through his mother´s lies and bigotry, he decided to fight back and provoke her. Imagine the enormous strenght of character he must have had if he was capable of doing that.
Nevertheless, I have always seen Regulus as a very meek, shy boy, eager to fullfill every dream of those who believed in him. He only found his strenght at the very end. You know, he very much resembles little Albus Severus Potter, Harry Potter´s middle child. He is just like Regulus - shy, nervous, meek, obedient, yet very bright and capable of listening. He needs a lot of love and somebody to believe in him, and with that, I bet he could do wonders. That´s it.
It is easy to see why his older brother, James Sirius Potter (see it, see where I am getting to, SEE IT..???), taunts him and considers him weak and inferior. It is because James Sirius Potter, like his elder namesake Sirius Black, is a stuck-up "original" who believes in himself and who can easily do on his own without any kind of help, but most of all, because of this all, he is also capable of SEEINGTHE TRUTH.
But little Albus Severus Potter, who is a shy dreamer, just like Regulus Arcturus Black needed it, NEEDS somebody who will hold a protective hand above him. He needs guidance, lots of love and lots of support. And then, you can do ANYTHING with him. You can mold hi and shape him like a clay, and he will do anything you want. that is why he went to Voldemort in the first place. He needed somebody who would take care of him, who would guide him.
And there is the point of the story. Rowling said she is considering another book, right? At first, she was like: "Never again!", but now she has started changing her mind. WHY DO YOU THINK SHE WROTE THE EPILOGUE IN THE FIRST PLACE? Let´s face it, it was dreadful, like some bad fanfiction, and the finished story did not NEED it at all.
BUT!!! Rowling uses the "Checkov´s gun" method when writing. Checkov was a famous Russian playwright who once said something along these lines: "If I write a play of TWO ACTS, and I show people that there is something SEEMINGLY unimportant in the FIRST ACT, but it is STILL on the stage, then it is there FOR A REASON. If I, for example, write that there is a gun on the table, IT MUST BE FIRED IN THE SECOND ACT." Which basically means that every seemingly unimportant detail you write in the story MUST GAIN ON ITS SIGNIFICANCE LATER ON. It must be there FOR A REASON, otherwise it is just wasting of paper.
So why do you think she wrote the SEEMINGLY INSIGNIFICANT EPILOGUE? The story had been already told before! Harry was alive, Voldemort was dead, THAT WAS THE POINT OF ALL SEVEN BOOKS! She already showed us that Harry was happy and well. So watching him do something as unimportant as escorting his kids to a train was UNIMPORTANT for the already finished plot. But Rowling did it anyway. A-ha..? And later on, she said that of all Harry´s kids, she likes little Albus the most because he is "the most interesting one".
Why would she do it? because the whole point of writing the epilogue was PREPARING GROUNDS FOR ANOTHER POSSIBLE POTTER STORY. It won´t be about Harry himself, I am sure; she is DONE with him. But she keeps on writing about little Albus. And little Al, when he is about to depart, HAPPENS to see little Scorpius Malfoy board the train. A-ha? And he is best friends with Rose Weasley, Hermione´s and Ron´s kid. A-ha? This clearly means WE HAVE THE NEW POSSIBLE TRIO, in case Joanne K. Rowling ever decides to write another Potter-related story. She only wrote the epilogue TO LEAVE THE BACK DOOR OPENED! :-D Ain´t that clear?
And it is ALSO OBVIOUS which House in Hogwarts she wants to send little Albus in. He KEEPS on asking about Slytherin, right? Considering that JKR does EVERYTHING POSSIBLE to hurt her characters (you love some character and she KILLS it viciously, just to show that you life is not fair), and Albus does not like Slytherin, it is a clear sign that it is EXACTLY WHERE HE WILL END UP. Plus, if you read THAT new HP story on Pottermore, when Harry´s family went to see the latest Quidditch world championship, his entire family was in red - EXCEPT FOR ALBUS WHO WORE GREEN.
So Albus is the new Regulus, and James Sirius is the new mixture of the old James Potter and Sirius Black. Also, little Albus is named ALBUS SEVERUS. So he is named after two wise professors, one a Slytherin. James..? Named after two common mischief makers. Albus is destined for greatness, it seems. And placing him in Slytherin would give JKR a great opportunity to take the story from another point of view. Because Harry Potter was a book about a Gryffindor´s POV.