Okay so to preface this, I loved a lot about this episode but um, I found it a bit, excuse the pun, difficult to swallow because:
1. I was actually getting physically nauseous while watching it. No, really, bile in my throat. D:
2. The gut-punch ending. Sam in detox. The revelation that Jimmy might still be alive in Castiel. Dean being pretty incredibly pretty in his manpain of pretty prettiness and his existential angst. ACH.
3. Okay, I'm also still oddly REALLY sad that the mortician died. I really liked him! I kind of wanted him to be their mortician friend and hang out with Castiel whenever Dean and Sam are out on a date busy.
This episode just left me all squirmy. It really was the grossest, GORIEST I think show has ever been. But okay! After I rewatch on an empty stomach I will still enjoy:
1. CUPID HANDSHAKING ASLKJHFLKSJHFS.
2. Sam and Dean making Castiel do things they don't wanna (like comforting Cupid). BWAHAHAHAHAHA Castiel is so their Mikey! LET'S GET CASTIEL TO DO IT, HE'LL BELIEVE ANYTHING!
3. Basically, everything Cupid did.
4. CASTIEL EATING! SAM EATING! DEAN... not eating?! I bet Jensen was just having a blast not having to eat ANYTHING this episode and he was just walking around, giving Misha and Jared (and the Donner Party couple) pointers on how to eat properly on camera.
5. DEAN CAME BACK WRONG. YES. Y'know when I think about it, he's technically stuck somewhere between demon and human in terms of his soul, yeah? We saw that a human soul was bright light, and demon souls are black smoke. I guess that a tenure at Hell's sleepaway camp is what literally turns your soul from light to black? OH HAI ANVIL METAPHOR.
6. On that note, and after waxing intellectual with my roommate a bit, maybe this is the impetus for Dean to say yes to Michael? He really was kind of reminding me of Nick back in 5.01, y'know being broken and empty inside, that dangerous kind of apathy.
Dangerous path he's going down. Oooooooh, I love it!
Addendum:
regala_electra is wrong on the internet. The song goes "BUILD me up, Buttercup". Not the dirty, dirty version she has in mind for Dean and Michael.