The opening - very intriguing and I loved the feel of it. Steven Moffat also gave us some more great Doctor lines that we can quote over and over again. I even made some t-shirts out of them. Check it out!
Clara and Missy were brilliant. They had just the right balance of their personalities, and you can really see Clara fulfilling her potential. It will be so sad to see her go.
The Doctor and his axe - I wish I could see Peter Capaldi and Craig Ferguson in their punk band! That whole "about to die" behavior was fun. And another touching moment with Clara. The chemistry between Clara and the 12th Doctor just gets better and better.
The ending is where things get a little wibbly-wobbly for me. I'm not saying there was anything wrong with it. Part of me felt it was great, but another part of me felt like something was off. I think I was thrown when I looked at the time and noticed the episode was almost over, when I felt like it had just started, and not in the "I'm enjoying myself so much that time flew by" way.
At no point did I feel the story was slow, but in terms of what was happening to Clara, the Doctor, and Missy, it felt like the "set up and developing phase" of the story, not at the "10 minutes left in the episode" point. That unexpected realization could have been due to being out of practice watching two parters. Or maybe it's because the reboot has never started with a two parter before. Again, it's like the question I had at the beginning of the episode, "Am I in the mood for this at the start of the series?"
Then there's the question of how the Doctor got back to the child. It will probably be answered in the next episode, so I'm not too worried about that - as long as it doesn't turn out to be something stupid like a dream.
Anyway, I guess I felt the episode was fine, and it has potential depending on what happens next week. But usually when I have to mull over an episode, it doesn't turn out to be one of my favorites. I had a definite reaction to every episode last series, so I'm just a little unsettled that I'm not quite sure about this one.
What do you think? Oh and also feel free to comment on my shirt ideas (see my storefront at http://teespring.com/stores/rebootwhovian). This was my first go and I'm hoping to make more in the future and will try to incorporate your opinions.