I was surprised and elated to see the return of Jo Harvelle in this intriguing episode. Sam gone bad was an interesting thing to watch as well. The episode definitely took a few turns that I didn't anticipate and therefore kept my interest.
That being said, the last we see of Jo in this episode may be the last we see of her character and that is a mistake. She and Dean had some great chemistry (go Alona Tal!) despite what other people said and it was so refreshing to see a female hunter character on the show.
I really like Dean and Sam. The acting is good (especially by Jensen Ackles who plays Dean) and the brothers relationship is an interesting one. However, the show would increase in depth and dimension by adding an exciting female hunter to the duo who could mix things up--both by challenging gender stereotypes and with possible romantic entanglements that could play out over more than a single episode. I mean these guys are heterosexual after all!
The writers may have been going in this direction earlier in the season with the introduction of mother and daughter, Ellen and Jo Harvelle in episode #2, but they seemed to have backed out after episode #6, No Exit, and my interest in the show has been deteriorating slowly since then.
I agree the mythological arch of Season 2 has been a little silly. There's very little suspense in the idea that Sam may be a devil child because then Dean would either have to waste him or Sam would become the very thing Dean hunts and neither possibility is likely or desirable. Sam must be saved and that's that. I really hope the show comes back to it's senses and returns to the fabulous idea of adding some new, important, female hunter/s into the mix.