I liked this quite a lot. I had hoped that the angels really were basically out to screw humanity over just like all other supernatural things, and while I'm not sure the claimed convoluted plan with Azazel and Lucifer holds up if you examine all details over the seasons, I'm not that attentive a viewer, and I like how the demons manipulated Sam and the angels Dean.
Ruby was awesome, and I'm somewhat sorry that she got killed, but killing her got Sam and Dean back working together. (Which admittedly is not a great trope when you look at the pattern that the evil, manipulative woman gets killed so the two guys can reconcile, and of course she's also one more drop in the large pool of slaughtered women in this episode, but I think I have mostly stopped noticing and stick with the shallow Sam & Dean squee... case in point, I wasn't even put off by the imagery of the killing as many were though I can see why that squicked people in retrospect.)
I also like that it seems that Sam and Dean may not end up on opposite sides after all for the following confrontation, and maybe will trust each other over the manipulative supernatural beings with various agendas again. I liked that Castiel didn't turn out totally spineless and brainwashed and helped Dean in the end. Better late than never. So I hope that in the next season he'll be around to help Sam and Dean fight Lucifer. Unless of course Lucifer needs to possess someone and will pick the conveniently demon-blood corrupted Sam. In that scenario they probably won't have time to sort out their issues. (I hope Sam at least finds out the phone call was the angels' or maybe Ruby's version.)
I wonder whether Castiel making a decision to side with Dean means he's fallen now? OTOH the upper hierarchy angels at least must have made a decision to hurry along the apocalypse at some point? It's probably best not to think about mythology workings too hard.
On a meta level I'm not sure that this trend to make the bad guys worse and worse over the seasons (from monsters with one demon, to demon hosts and angels and now Lucifer himself) until it's now all about the cosmic battle is a great idea, but maybe there'll be some kind of reset after they sorted out the apocalypse or something, that allows some regular monster fighting again.