Basically, after he drank some infernal plasma, Sam had whatever ability he needed to defeat whatever demon was in front of him. He became a walking deus ex machina, like a demonic superhero. This was all contingent on him drinking the blood, though, and once he stopped he no longer had any of these abilities.
Sam loses his demon powers, claiming that the force that transported him and Dean onto the plane cleaned him up. He feels tremendous guilt for starting Armageddon and soon learns his acts have revealed a destiny Dean will be the vessel of the Archangel Michael to fight Lucifer.
Evil! Sam is the name given by fans to Sam when he was possessed by the demon Meg in 2.14 Born Under a Bad Sign.
Supernatural's Sam was thrust into doing evil things by way of possession multiple times but also acted as a villain through his own choices.
Sam was always meant to be Lucifer's true vessel in his apocalyptic fight with Michael, but Sam steadfastly refused. After finally giving in, he was able to turn on Lucifer and force them both into the cage at the end of season 5.
In a future God shows Sam where the Winchesters and Castiel succeed in locking God away, Sam is eventually turned into a vampire on a hunt gone wrong. During a final confrontation with several hunters, including both Jody Mills and Bobby Singer, Sam is shot in the chest by Jody with a dead man's blood bullet.
While masquerading as Ezekiel, Gadreel inhabited Sam Winchester, as a way to heal the hunter and himself, but also to hide from Bartholomew and Malachi. Crowley managed to torture the angel enough for the demon to enter Sam to make him expel Gadreel out. Gadreel moved on from Sam and entered his previous vessel.
When Dean died, he left Sam alone, and he hasn't quite forgiven himself for that. Though we know that Sam is okay (he eventually marries and has a son, whom he names Dean in honor of his late brother), Dean is still the over-protective big brother he's always been.
Unknown to Sam, the ritual makes Dean human enough that he is able to escape and he stalks Sam throughout the bunker. However, Castiel finally arrives and subdues Dean. They are able to successfully complete the ritual and Dean is returned to being human, but retains the Mark of Cain.
Power: Dean
Even if Sam is taller and generally seems more fit, Dean has demonstrated on many occasions that he's the more powerful of the Winchester brothers.
Within a moment's notice, Lucifer dropped a major bombshell on Sam — and the entire "SPN" fandom — by admitting HE was the one sending Sam visions of the Cage, not God.
After his brother is killed by Jake Talley, a desperate Dean Winchester summons a Crossroad Demon to make a deal to resurrect Sam. The demon negotiates a deal where Sam is resurrected and in exchange, Dean's soul goes to Hell in one year.
Using holy fire, Sam is able to cure himself and then save the remaining people in the town. Returning to the bunker, he and Dean find Castiel begging for help.
When Dean had first met Ben Dean considered the possibility that Ben might actually be his son. Lisa confirmed to Dean that Ben wasn't his son and his similarities to him was due to her 'type' that she hooked up with that Dean had fallen under.
Season 10. Enjoying his time as a demon and killing several of Abaddon's loyalists, Dean eventually kills a man called Lester Morris and uses his newfound demon powers to confirm what Crowley told him about Sam.
Sam has certainly been through the wringer in his lifetime. His mother was killed because of a demon deal to save her husband that allowed the demon Azazel to come into his room while he was a baby to turn him into a human-demon hybrid that gave him special powers.
After all, despite his intentions, Sam did the unthinkable. He betrayed him for a demon. Dean tried to see past it and focus on task but the hurt was too deep and the betrayal too raw. He couldn't forgive.
After Dean got turned into a vampire by Boris, he expected to have to be killed but Samuel informed him of the cure when he arrived. Samuel showed Dean the journal entry on the cure and assured him the cure would work despite Dean's skepticism.
Sam: Let Dean Become A Vampire
If not for the cure, Sam was risking either Dean be stuck as a vampire for a lifetime or killed to avoid that very fate. Sam with a soul never would've let it happen, but Sam still did this, making it one of the worst things he's done to Dean.
Dean later briefly possessed a pair of Black Eyes while he was a Demon. Since separating from Sam, his appearance has become more scruffy and unshaven; his hair has also grown out a bit. In Let the Good Times Roll, Dean gains a pair of Angel's Wings due to his status as Apocalypse World Michael's current vessel.
Fitting: Ended Up In Heaven
Most fans know that whenever a person dies, they either go to Heaven or Hell. Because Dean died several times in the show, it was only fitting that he not only died in the show's finale but that he was rewarded for his job as a hunter by going to Heaven.
This meant that viewers got minimal details about Sam's life after Dean died in the Supernatural series finale. In Sam's old age, the Impala can be seen under a sheet, implying that he stopped hunting.
Trivia. There has been hints by many characters that Castiel is God's favorite angel, due to his resurrections and improvements to his powers by the latter's hands. Castiel's resurrections has caused him to be known as God's chosen as he has earn the envy of many angels.
Michael is the first and oldest of the four Archangels created by God, making him the very first angel ever created, as well as one of the oldest and most powerful beings in the universe.