I have never used microwave popcorn before - i make my own in a pan. But I have tried Butterkist for the first time as I had DS's friends round for a Ben 10 film morning. It was a total disappointment and a complete waste of money!
I would say that less than half the corn in each bag popped, so we got a measly amount. It compares v badly to ready made popcorn in a bag, never mind the negligible cost of ordinary corn kernels popped in a pan!
I followed the instructions exactly, and it was in for 4 mins on 750w in a microwave that is not old, and works well.
I am tempted to send the 3rd pack fom the box back with the kernels that didn't pop.