Unlike many I loved the episode.
I think it tells us a lot about Sam and Dean and finally John seemed like a real person that had a real life (just like his boys), women included.
John never wanted this life for his boys and when he was provided a third change, he took it and had Adam live a normal life. Unfortunally, he was wrong about not training his youngest son. When Sam and Dean meet monsters they are able to deal with them, Adam wasn't and so he got killed painfully. Poor guy!
We also see that Sam has become more like his Dad. He now sees that the best way of keeping someone save is to teach him how to take care of himself. Dean on the other hand doesn't get this until the end of the episode. We also get to know that Sam's tired of being the youngest. He knows a lot and wants to share his knowledge. While Dean doesn't want anyone to be cursed with this life, Sam is eager to get some help, to pass on the legacy.
Jeolousy turns into pity. Sam and Dean may never have had Adam's life but they are still alive because of what their Dad taught them.