Not much of this made sense, and even the bits that made sense didn't particulary interest.
Smith acted his socks off at the end to try and save it, but I'm not sure how the monster-thats-actually-a-sun was defeated by a leaf.
So the seven planets now have no sun?
I love Doctor Who but this was right down there with the worst.
I'm not quite remembering it all, so here goes:
The sun god creature was a parasitic lifeform that every thousand years wakes up and needs feeding with psychic energy. In particular that generated by negative emotions and memories; the aliens use a girl and implant all of the stories of their culture, which I then presume causes the appropriate mental conditions required to make this tasty sacrifice work, and offer her up to it so that their god will be sent back to sleep.
However thanks to his interference in this process, the Doctor himself instead offered it his thousand or so years of pent up negative psychic energy to feed on, and tried to gorge it to sleep again, if not, to death. The Doctor almost got it all the way there, but it needed just an extra push past the post, which Clara provided by offering up her family's life story, embodied by the leaf that allowed her parents to first meet.
I've probably got some of this horribly wrong.
I still cant work out how the seven planets survived without Sunface Angrygod though. Also, was it really necessary to interfere? The doctor took a massive chance here I thought. The only person that really seemed in trouble was the little girl. Everyone else on the seven planets had been getting along just nicely the last few millennia - they didnt seem particularly enslaved or anything. They just sacrified a little girl every thousand years or so to keep the peace.
I mean, it all turned out alright in the end but it could have ended up wiping out SEVEN PLANETS. Im not saying its right but I doubt Picard would have intervened...