The episode wasn't too bad until the ending, which turned into a cascading failure.
First, the deus ex screwdriver has finally reached the point where I can no longer tolerate it. It's gotten pretty bad over the past few seasons in terms of being a magic wand that can affect any inanimate object in any way the writers want; but now the Doctor can just wave it emphatically in the direction of people and have it serve as an impediment. It only fails to work when the writers decide it would be more dramatic for it not to. They've dug themselves a deep, deep, deep hole with it and they show no interest in getting themselves out of it.
Second, there was the Doctor's interminable-but-empty-and-ultimately-meaningless speech about "take it all".
Third, there's the leaf. Which, as you say, makes no sense whatsoever. The thing can eat an entire kid without missing a beat because of the "infinite number of possible futures" it is directly snuffing out, but a leaf which merely represents those possible futures is the thing's kryptonite? (And even that doesn't make sense, because that's not actually what the leaf is established as actually representing earlier in the episode.) Out of the millions of people who have offered up millions of sacrifices over the past few aeons, nobody has ever given up something that was sentimental because it was important to their dead mum until Clara came along? Complete nonsense..
