First, let me say:

. Eloquent, no?
Upon watching this for the first time, my brain decided that all the clips were from the upcoming episode and shut down for about 6 minutes, leaving my mouth hanging wide open.
When I watched it the second time (after rebooting, of course), I kinda woke up the entire *sleeping* household by squeeing till my lungs gave out. Note that I saw this trailer late at night.
The third time took me about 30 minutes to watch it because I was freeze-framing every half-second. And yes, that
is Castiel duking it out with Uriel.
Finally, on the fourth (and every subsequent) viewing, I could think somewhat clearly and I realized that it looks like they sprinked some old clips in there, along with a bunch of mixed ones from future episodes, not
just 'Death Takes a Holiday'. Unless I'm mistaken, that hospitalized Dean scene looks like it could belong in 'In My Time of Dying', but I don't remember Dean from that camera angle precicely... if that makes sense. And the Sam/Ruby love scene looks like it was taken from 'I Know What You Did Last Summer', but flipped. The explody blue light shot could be from 'Are you There, God? It's me, DW' when they vanquish the 'witnesses', but it looks slightly different from when I watched it... in the trailer, looks like it's coming from someone (Sam, anyone?) sitting down, not standing, like in 'AYTG, IMDW'.
This trailer made me think: Umm did anyone think that maybe Dean might be the one to dabble in the dark side? Beyond the giant (metaphorical) entity of 'Evil-Sam' looming up ahead (being set up by having him use his powers and the whole contrasty Dean/Angel & Sam/Demon hookups), did I ever consider that it could be Dean that goes darksdide? I mean, a weekend in Hell is bound to mess with your head. Just a little.

Then there's the Alistair torture (!!!) thing. And the Reaper saying that good things are in store for Dean and all. And this is Death we're talking to, mind you, and might have very different ideas of what 'good things' are. I remember that nicey-nice attitude from 'In My Time of Dying', Miss Reaper... don't think I don't!
Extremely excited for a darker Sam, (as well as a darker Dean, for that matter!) and can't wait for Castiel to pop back in... that character looks like it's gonna kick some butt when he comes back! *dances* If this trailer isn't the perfect way to keep fans biting their nails for what's to come, I don't know what is!!