It's odd watching a programme I used to love develop into its final form more than a decade later. The second season of Supernatural starts with the brother and father Winchester in hospital and Dean on the brink of death, only by selling his life for his son's does John Winchester keep both the protagonists in the running. This will become an annoying running theme later on, but the episode of Dean being a ghost in a hospital is fun while it lasts, ending with a cliffhanger about Sam's powers which pay off halfway through the season. Sam's powers and their demonic origins are a major plot thread for season two, which has the interesting effect of, conversely, throwing Dean into the protagonist spot, usurping his brother from the previous season. As I reflect on Supernatural, it seems to me that Dean is the main protagonist, as he is often the one reacting to change as much as the audience and, aside from in Season 5, has nothing "special" over any other hunter or monster.
Demons are the most common monster this time around, as Yellow Eyes is gathering the super-powered children, like Sam, to open a gate to Hell and only the handful of hunters with recurring actors can stop him. That reminds me, there are other hunters this time around, with a whole truck stop full of extras and even a rival hunter I can't remember the name of who is a little too gung-ho about all of the murder he's doing. Grey areas start to enter the narrative, with bad hunters, good vampires and factions within Hell's ranks, which helps add tension, but won't play out until later seasons. There is a really clever episode where a ghost is unaware she is a ghost and the brothers need to help her crossover, which is worth a look all on its own and is considered one of the best by fans online. Also worth checking out, for my money, is "Hollywood Babylon", where the brothers work on the set of a b-grade horror film directed by Supernatural's producer, it's fun and not too meta.
The plot of Yellow Eyes "seeding" children to have powers later in life isn't too far from an evil version of Nick Fury's "Caterpillar Program" from Secret Warriors, and would work nicely in any Ghost Rider, Constantine or BPRD scenario you were putting together, but, once again, the "monster of the week" content is more suited to something like a roleplaying game. Even with the distance of time and presence of newer content from streaming, the broadcast series style of Supernatural remains really watchable, especially from here on out as the cast and crew are established and the balance between the serious moments and gags is balanced like a fencing sabre most of the time. If Supernatural has a weakness, beyond budget and stunt-cast guest stars, it's that the core cast never expands much beyond the brothers Winchester, and I do enjoy a good ensemble.