At its core, honorary Winchesters. Sam and Dean will do literally anything to help their makeshift family, and their loyalty and sacrifice aren't one-sided.
Many of their values stem from John and their upbringing. John is a very complicated character. Due to these complications, there are times when he's overrated, and there are plenty of times when he's underrated.
Overrated: The Protector
John cares about his family, and he tries to protect them. In some ways, he's successful. Sam and Dean probably lived to be adults partly due to John's influence. However, John hides things from Sam and Dean. Of course, his intention behind this is to protect them, but instead, he alienates them.
Then Adam is an even stronger example of how John as the protector is overrated. Adam is John's son, someone whom he kept in the dark about the hunter-life. On one hand, he wants to protect Adam, to give Adam a more normal life. But on the other hand, he doesn't prepare Adam for threats, living him completely vulnerable.
Underrated: The Teacher/Trainer
Unlike with Adam, John prepared Sam and Dean for a hunting lifestyle. The Winchester brothers learned valuable skills that would not only help them kill monsters, but would help them survive to fight another day. When they were older, he had them hunt with him.
It's because of what he trained and taught them to do, that they survived many threats. Additionally, they were able to build upon his lessons in order to become even better hunters.
Overrated: Connector to a Network of s
John has helped people, and he's connected to them. He's even connected to people he served with in the war. In the first season, fans see Dean and Sam following up on those s. John had left a message that if his s can't get a hold of him, that they should call Dean.
However, he didn't maintain a network of informed s for the boys. They met other hunters, but John had burned bridges with many of them. Thus, the boys had to develop their own relationships with these informed s, and show that they were more than just John's sons.
Underrated: Man of Letters
John comes from a lineage of the honorable Men of Letters. His father (Henry) was one, but John became a hunter instead. He wasn't trained to be part of the Men of Letters, yet he's a smart and keen researcher. Even Ash is impressed with how John has been tracking the yellow-eyed demon.
When Henry time-travels into present, Sam and Dean share John's journal with him. Henry is a great example of a Man of Letters, and he's impressed with the extent of research that John did. John's intelligence was also key because he could figure out how to kill monsters that seemed invincible.
Overrated: Hunter
This one is a little more complicated because John was known to be a great hunter. Even those who criticized him, they still recognized his ability. The yellow-eyed demon once said that John was actually more of a threat than the Colt. So, then why is John being a hunter overrated?
For John, hunting was killing monsters and fighting. While he could still physically take his sons, he lacked their more nuanced understanding of hunting. In Season 8, Dean tells Krissy (a young hunter), "Hunting isn't all about killing and revenge." Both brothers understand that hunting is also about saving people, even freshly-made vampires. It's unlikely that John would've acted with the same comion.
Underrated: A Just/Righteous Man
When Dean goes to hell, he's tortured horribly. He's constantly asked if he would become one of the torturers instead, thus freeing himself from the pain and suffering, but having to give it to others. While he resists for a long time, he eventually succumbs to it. So, he ends up breaking the first seal needed to free Lucifer, "The first seal shall be broken when a righteous man sheds blood in hell."
All along, this first seal was meant to be John. However, John never gave in. He was in hell longer than Dean, suffered more torture, but his inner strength and principles held him in place.
Overrated: Fatherhood
John did teach two of his boys to be strong and knowledgeable about the supernatural world. While it's clear that he loved both of them, he clearly favored Sam--protecting him more from the knowledge of monsters than he did with Dean. Poor Dean was overlooked a lot and even neglected. He could never be good enough for his dad.
And Sam, while the favored son, wasn't ed either. Sam didn't want anymore of this lifestyle, and John blew up in anger. That he loved his sons was never the issue, but he didn't give them the best of him. Additionally, he didn't seem to care to know them (especially Dean) beyond hunting.
Underrated: Potential for Reflection
John does own up to his faults. He tells Dean that he knows that he put him in an unfair position, "You know, I put, I put too much on your shoulders. I made you grow up too fast. You took care of Sammy. You took care of me." Unfortunately, this heart-felt conversation happens before John dies, but it does show that John could reflect on his behavior, acknowledge it, and grow. Later, he also acknowledges his past with Sam, too.
He wasn't the best father, but he did his best.
Overrated: Honoring Mary's Memory
John lives his life for Mary, and he makes her death the focus of Sam and Dean's lives, too. He researches ways to find the demon that killed Mary, so his inner motivation is revenge. This is understandable, and it could be seen as a way to honor Mary's memory.
Still, would Mary have wanted her children exposed to this lifestyle? Exposing them to monsters at an early age and neglecting their basic needs for attention and affection, did not honor Mary's memory. It was the opposite.
Underrated: Family Love and Loyalty
While John may not always have been the best father, he does love his family. He's extremely dedicated to Mary and his boys, and is more than willing to sacrifice himself in order to save them.
When John is brought from 2003 to 2019 in Season 14 for a day and finds out that by staying, Mary would disappear, he says, "Me versus you mom. That's not even a choice." Still, they all get one meal together, and John beams with the love he feels for his family. John is serious about is his love and loyalty to his family. Luckily, this is a trait that Sam and Dean share.