I will put it under the cut because it's spoilerific.
First some fun things:
How cool was it that Mitch Pileggi of X-files played Dean's grandfather Samuel and his Grandmother was Deanna - Hah excellent names - Dean is a girl.
Dean convinces dad to buy the Impala that he eventually gives to Dean - nice touch.
The crack about cell phones from Star Trek.
Dean thinking his mom's hot and then talking about going to hell...again
The diner scene was so reminiscent of 'Back to the Future' when Marty sits next to his dad and someone calls their last name and they both turn. Bet they did that on purpose.
Now the sad stuff.
Mary and her family turned out to be hunters - inspired. It explains why Mary knew the Demon when he showed up in Sam's nusery.
Everything fit together like Clockwork.
Dean couldn't change it and in a way it seems he helped the Demon find Mary - or is that just the way the Angel was able to show him what happened. The demon caught wind of her simply by being in the area or was Dean 's time travel the reason why why Azazel never killed Dean - he had to make sure Dean went back in time to tell him about Mary - maybe. Sometimes time travel makes my head hurt
When Mary wished her children would never be hunters and Dean begged his mom not to get out of bed on Nov 2nd - It broke my heart. Dean gave up the single manly tear - jesen is awesome with that.
YED killed John and used him to force Mary's hand and make the deal. We know that Azazel's plan is still in motion thanks to Sam and we know more why Angels are interested in Dean.
Overall this was a fantastic episode - I love it when the canon makes sense
On a personal note - I'd squeed like crazy when YED complained about Red Tape (The title of my first Immortal!Dean Story) - LOL See I knew there was red tape in Hell and Dean is Immortal