After the cliffhanger at the end of last week's episode, I was expecting a continuation from the Leviathan/Cas story dominating the previous episodes. Instead, Dean and Sam escape from the hospital with help from still-alive Bobby in the first couple minutes of the episode. So much for cliffhangers... This departure pushes Supernatural into monster of the week mode which we haven't had in a while.
Although the Sam and Dean dynamic doesn't feel particularly fresh, as it's about the 10th iteration of the deceiving plot, the monster story was very interesting this week. Through a series of flashbacks, we see Sam a kid meet this girl Amy, tied into the current case Sam ran off to work on. The monster in question is one of the most sympathetic yet, no doubt helped by Jewel Staite, and we see Sam connect on a deep level with this supposed monster. Both their parents made them what they were today, on completely opposite sides of the monster spectrum, but they can still live with each other. Of course, Dean comes and messes things up.
It's impossible not to look at Dean as a moron when he does kill Amy. Amy killed her own mother to save Sam, takes brains from dead bodies, and only started killing again to save her son. She's obviously not a bad person. If Dean is going to kill her on the principle that she will kill again, he must kill the boy as well who no longer has a mother to provide him with food. Otherwise, Dean is just an idiot who's fine letting the boy go and kill more people.