I liked this episode, because there were so many creepy/unsettling scenes. The scene when Sam and Dean lure Jack in the box, of course. The scene when Sam asks Dean to talk about Mary, and Dean brushes him off and says "isn't that what we just did" (from memory -- may have gotten that quote slightly wrong). The scene when Jack mesmerizes all those churchgoers and curses their group leader to be "eaten by worms" (everything about that curse was horrifying). All-in-all, this was a legitimately scary episode, which I always appreciate from this show.
I was very confused by Jack making angels out of people, too.
The interaction between Jack and Duma was interesting to me in general, because Jack was completely obedient and seemed happy/relieved to be following her orders. The thing that I think is most interesting about angels is that they're made to be obedient in a way that humans aren't, and I wonder how that comes into play with Jack. He seemed really obedient in this episode in a way he hasn't been before, but maybe that's just because he's at loose ends.
Anyway, that was clearly actual!Lucifer that was talking to Jack, and not some figment of Jack's imagination. There is no way that Jack would know Lucifer well enough to have him behave so true to character, and some of the things that Lucifer was saying just aren't things that I think would occur to Jack anyway. That said, I don't think that Lucifer is controlling Jack or even manipulating him that much -- he seems like he's just sort of harassing him. So I don't really know why he's there, aside from as a dramatic device to give Jack a conversation partner.
Jack seems totally lacking in compassion/empathy now, which is a fairly new thing for him. Dunno how anyone can come back from that. I think that he (and the bit of Lucifer that's hitched a ride in him) will have to get sent to the Empty. I'm unspoiled, that's just apparently where angels go when they need to be locked up permanently, aka, killed.
Anyhow, putting Jack in the box wasn't a bad idea, although how Sam and Dean did it was uncomfortable and creepy as hell (and interesting/fun to watch because of that hahaha). I don't buy that Jack would be able to bust out of the box so easily, either, because I would think that without a soul to supercharge his grace, Jack would be just at regular angel strength (if that). But whatever, this is how the show is playing it, so I'll roll with the punches.
It's interesting that Sam and Dean have now "betrayed" Jack by telling him the exact same pack of lies that Jack wanted Mary to tell him (that everything would be OK, basically). I think it's possible that after Jack killed Nick, Lucifer possessed him and that possession was a factor in Mary getting killed. But at this point, after Jack's weird confession/apology about Mary's death being an accident, I don't think that Jack can be absolved. He openly accepted at least some responsibility for it and wasn't remorseful enough, so there ya go.
You know, I had actually been thinking that at least some of why Jack was so upset about killing her was because he felt guilty, missed her, etc. But this episode made it clear that he really didn't feel any of that. He just wanted to be back in Sam and Dean's good graces, he apparently didn't care about Mary in her own right at all? That's pretty chilling.
Honestly, I thought Cas was the most relatable (to me personally) out of the characters in this episode, though. I mean, he took Mary's death seriously, but he couldn't shut off his love for Jack like a light switch. I think that all their reactions were true to character and made sense, but I thought Cas was pretty sympathetic in this one.
WTF was up with that bizarrely well-attended wake at the beginning, though? And Bobby's entrance with the ax-throwing and the guitar riff? LOL terrible. Also, just not the right tone for the rest of the episode at all. It makes me laugh thinking back on it.