Turn out alright again? As if! Yes, Dean gets resurrected by the angels and reunited with Sam, but the time between took a toll on both of them. Sam stayed with Ruby who gets him hooked on demon blood to make him more powerful. Now he's able to exorcise demons with his powers, but it really made him an addict. Dean, while in hell, broke under the torture and became a master of the craft himself, thus breaking the first of the 66 seals needed to free Luzifer from hell. That's right, freeing the fallen angel, master devil himself. There's a number of biblic rituals/happenings that can be used as seals, any 66 of them broken will do.
Lucky for the Winchesters, they got angels on their side to help them. Well, at least some. Castiel, the one who rescued Dean from hell, issues warnings and a helping hand. The boys also find a woman named Anna in a mental health institute, who was talking about the 66 seals and is able to tune in with the angels' mental radio. And that's because she's actually an angel herself, fallen and seperated from her grace. Sam, Dean and Castiel help to recover it, but have to go up against other angels in order to accomplish the task. The good guys, my arse! Anna encourages Castiel to listen to his heart, bringing him fully over on the Winchester's side.
In the end, the boys can't stop all the seals from breaking, leaving only über-demon Lilith. Thinking they have to stop her from breaking the final seal, the boys kill her, thus breaking the last seal and freeing Luzifer. Furthermore, it turns out it was Ruby's plan all along to make Sam powerful enough for the task, so it's a good thing she got what she deserved in the end.
Favorite Episode: Wishful Thinking, because that poor teddy bear is just... LOL