This is a balanced episode that provides everything a good episode does. It has a nice reveal of the ongoing story. it has a few chills...the rapid ghosts are really memorable and creepy. It has a central image that is memorable. The blue fire burst for when the spell is complete stays with you. It has some choice Dean melodrama of him trying to work through the problem of evil. Etc.
Unfortunately the show feels the need to insert flashback material to remind viewers who the ghosts are. It was never really needed but on re-watch it is distracting as it breaks the atmosphere of the set-up. Furthermore, because the episode when Bobby failed to save the young girls doesn't exist there's nothing to cut back to in his case. So it is quite awkward in the overall construction as the scenes explaining who the young girls are missing.