Impressions
Very good episode. The episode integrates stories from the brothers' childhoods into the plot of the current storyline, giving the audience deeper insight into their characters.
Critique
A unique monster in this one, the Shtriga, which feeds on the life energy of its victims. But the bigger draw is a glimpse into what life was like for the Winchester brothers growing up, after their mother died and their father began "hunting". It gives us an idea why Dean is so protective, and also why John was so hard on his sons.
The story doesn't advance the longer story, but has its tense moments. Writers revert to the old "put innocents in danger" trick.
Trivia
Written by Daniel Knauf. Check out the bit about his pseudonym. Knauf also wrote for Carnivale.
The director was Whitney Ransick, who directed episodes of ER and Smallville, along with other shows.
Once again, Wikipedia doesn't disappoint. More info on the Shtriga.