So I actually really enjoyed that. I got teary eyed several times.
It was just the right touch of nostalgia for me - I really liked the way the Chuck narrative wove in the threads of the past seasons to show how things got the where they are.
Also, I think it goes without saying that I loved Dean's whole, "Then he won't die alone," thing, as well as it being him and the army man in the ashtray that brought Sam back.
RE: the end - I think it was real Sam. I think God brought Sam back (that was def. a Sam expression on his face, not a Lucifer one, and props to Jared for being able to show such a difference). And now we're in the perfect position to have some angsty "You're better off with Lisa and without me" "No I'm not" "Yes you are" fighting next season. (Although that streetlight going out was quite coincidental, no?)
Also, I loved that there were totally 4 main characters in this episode (as it should be): Sam, Dean, SamandDean's Relationship, and the Impala.
Long live the Metallicar.
All in all, 2 thumbs up.