Well, the "Sam quit" story was exactly as stupid as I feared it would be. I don't see why they couldn't just have had him hunting on his own, searching for a way to find Dean or rescue Kevin or even just killing monsters of the week while Dean was locked in Purgatory. All it was there for was to cause angst between the brothers and honestly I think that's something we've had enough of.
I'm also not too fond of Kevin. That scene with his girlfriend being killed was entirely overdone, and I don't like that he can outsmart Crowley when the Winchesters, who have years of fighting demons, could not. And being King of Hell shouldn't Crowley be strong enough to resist Holy Water? Wouldn't the earthquake he used to shatter the Devil's Trap have spilled Kevin's water bucket?
They also wrote off Castiel again, which I don't like, but I'll wait until we learn more about what happened to pass judgment on that. It could still potentially be a good story even if I don't like where it's going.
What I did like about this episode was Dean. The scenes in Purgatory were great. I'm intrigued by his new vampire friend and I can't help but feel he was entirely justified yelling at Sam when he got back. Wish he'd be a bit more open about what happened, particularly involving Cas and how he escaped, but I guess we just can't have anything in the first episode. That's probably my biggest complaint about this episode (well, second biggest after Sam quitting) there weren't any surprises. We pretty much knew everything that would happen from interviews and previews months before the episode aired.
Overall not the start I was hoping for for season 8, but I'm not going to let one mediocre episode condemn the entire season. I just hope they don't drag out the Sam plot like they did Kaylee Amy in season 7.