I thought with the ghost woman it was incredibly easy to see how she did it. As @CalmConfident says above, fake lid in box so she knew exactly what photo would fall out.
I liked the primary school act, missed that they got the golden buzzer. Was that David? Very like the Sainsbury ad and the film Nativity. The headteacher even looked a bit like one of the actors. The bit with Dec in the bin was a genius touch.
One act I didn't particularly like was the ventriloquist. It wouldn't have been as good with just 2 regular audience members, or without David hamming it up. I'm sure there's been similar on before yet Simon said it was original !?
And talking of unoriginal acts - those 2 balancing on heads? Didn't we have exactly that last year?