I for one really liked it!! I know a lot of people said the plot was all-over-the-place, but, really, it was a wild ride from start to finish and it never really felt clunky, because I was always entertained, so I really don't think it matters that much.
Also, the moral dilemma regarding the Doctor and Davros reminded me a lot of a certain Classic episode -- Genesis of the Daleks -- so I was very amused to see one of the key moments from that episode shown in this one when Davros was reminding the Doctor of all their past encounters. Speaking of which -- there were a ton of awesome throwbacks in this episode, which I really liked. Most notably, I loved seeing the blue-and-silver Daleks, which were the very first Daleks ever to be seen in the show, except that they didn't look blue-and-silver because the show was in black-and-white then. So it's rare to see them in-color in a real episode! Also, that one line when UNIT was trying to find the Doctor about "three possible versions of Atlantis" killed me, since it's a reference to the show's horrible continuity and the fact that they've had about three different Atlantis episodes that all feature completely different versions of the city and don't mesh with each other at all. XD
I was really surprised to see it end on such an intense cliffhanger, too, since normally season openers don't have cliffhangers at all. I keep seeing a lot of people shit on the cliffhanger like "well obviously Missy and Clara aren't actually dead", but, if you ask me, that's not the point! I know that they will survive -- what I want to know is how and, more importantly, what really got me was the Doctor going back in time to 'exterminate' Davros. Yeah, it's probably a safe bet that Davros won't actually die, but you can still feel the intensity in the whole scene and you want to know how it all plays out, and that is what makes a good cliffhanger good, imo -- and not simply wondering whether or not certain characters will die when you know they won't.
Oh, and Missy's fantastic as ever. I lost it at the "I'm back, big surprise" line, since no one ever really thought she was dead at the end of season 8 and it's been pretty clear that the Doctor Who team knows that we know, since they haven't at all tried to act like it was a secret that she was coming back. Additionally, I found it a bit odd that Missy seems to be acting sort of like... a companion? I mean, her and Clara almost seemed to be acting like a team half the time and they're both filling a sort of companion-ish role, even though Missy is still decidedly not good. :P Oh, and "Davros is your arch-enemy now?" really cracked me up, as well. XD
Oh, and rockstar!Twelve was just as glorious as the trailers made me think it would be. XD