So much continuity! And so deftly woven in that even though I was going "oh, continuity!" while watching, I can't pick out specific instances in retrospect.
I was a bit nervous about how they'd handle Mary, but I liked this. She's bewildered but not baffled, and definitely not in distress. And, as I would have hoped--had I thought this far--she'd heard of the MoL as an urban legend-type-thing, and is able to roll with some of the punches because of her family's background as hunters.
Sam's bare toes (and Jared's ability to act with his feet).
The Mystery Spot billboard--completely unnecessary, entirely delightful.
Thos magic brass knuckles--even though Sam and Dean (and Cas) get taken down by women who are significantly smaller than them, in both cases the women have a significant technological/magical advantage.
That the guys keep a gun hidden under the table in the war room
Wet Sam (sorry Sam, you're just so lovely when wet); also, the jerry-rigged setup for his involuntary shower.
Dean obviously holding things together for Mary's sake--except for the phone incident.
Dean reusing the traffic camera trick that Frank taught him (oh hey, there's one of those continuity moments).
Sam's slight of hand with the broken mirror.
The ending music cue--combined with the gorgeous camera work and Jared's acting, I was definitely tearing up a little.
I know some people were irked by them, but I loved the bitchy demons. Dabb stuck them in at just the right points to keep me from freaking out over what was happening with Sam, and used them to remind us that demons can switch bodies willy-nilly.