So, I'm doing a bit of research for a friend. All I want to know is, in your opinion, which two episodes over the entire series best represents the series in all it's glory as a whole, and maybe a little explanation why. Any and all answers welcome
The Pilot- I agree with Lilah that it has all of the ingredients that make the show so special: the theme of family, the family business, the MOTW, and best of all that incredible, intense, complicated relationship between the brothers. It beautifully laid the groundwork for the first five years.
Swan Song- Unbelievable resolution to those first five years. I had a catch in my throat from Chuck's first voice over. I get emotional every time I watch it. From the framing device regarding the impala to that montage at the end that allowed Sam to regain control, it was a perfect hour of television.
So I think your question is as much what is the the most typical episode that you could show someone and say 'this is Supernatural'? Obviously that is next to impossible over 10 seasons but here are the two that came to mind for me:
People dying in the teaser
The boys fighting over their father
Dean being the good son, Sam being the rebel
Sam making his own decision about moving on - I don't know that it ever occurred to me before but him getting out of the Impala in the middle of the night to walk, Dean telling him that he should do what their Dad wanted and Sam refusing to do anything except what seems to him to be the right thing is probably meant to be an exact parallel of what happened the night Sam left home. (I hope this group of writers never write that flashback....)
Dean using an alias, annoying the locals by being a smart-ass, rescuing the next set of victims.
Reference to using Sam as a puppy-dog
Sam meeting a demon who wants to manipulate him.
This episode has direct links all the way back to the basis of the mythos of the show (as Meg is related to Yellow-Eyes) and all the way forward to the end of Season 2 storyline-wise - a pretty good arc.
Dean needing a researcher, sucessfully finding a good one but ... discovering that Sam is the most reliable (gets knocked out and nearly sacrificed)
Dean realising Sam is his own person and his decision making skills are actually pretty good - and both saying so and making an apology without necessarily having to say it (a skill he could relearn these days ...)
Sam reluctantly using the less honest of his hunting skills (steals car)
Sam deciding they are stronger together as a team.
Sass between the brothers.
Driving off in the Impala.
This episode has literally everything that grabbed people about the show. It is a pretty great little episode.
Then at the other end of the spectrum we have Sera Gamble and Ben Edlund and some VERY nervous actors ....
The French Mistake
Meta has been a part of the show for a long time.
Fans love behind the scenes stuff.
Fans know enough about everyone on the show to get about 85% of the jokes
Crew has been together so long the other 15% of the jokes are like the gag reels
'You married fake Ruby?', Locks and keys, Castiel having a storyline (!), Balthazar, Bobby's place ...
and, most of all, self-awareness (Why are we taking ourselves seriously?):
I think if you wanted to introduce someone to SPN and also explain why the SPN fandom is famous on Tumblr for having a 'gif for everything' - you would probably cover most of it with these two episodes.
The Pilot though it's an excellent introduction, you don't quite have a feel for the characters quite yet and the brothers have a long way to go before their relationship really develops.
Dark Side of the Moon gives a large amount of information about the boys from their childhood memories, the differences in their personalities and values and informs us that Dean and Sam have died many more times then we even knew about. It has a lot of hidden secrets.
Swan Song gives us the Biography of the show and more hidden parts of the lives of the boys, basic day to day and life events that they don't really bring up like the boys being KU fans and what they do when they aren't hunting and the importance of every aspect of the Impala.
I would say the pilot episode. I agree with the others, that is has all the ingredients that make up Supernatural. And I started with the first episode and it sucked me in immediately. I personally hate the meta episodes, so I wouldn't recommend those. But I suppose that a lot of others do.