I've only been once.
BB9 Launch, when I was 18.
It was fun, but that was when the crowds began to get smaller, so it looked quite depressing.
My brother went to the BB5 launch, and my sister went to one during a BB7 eviction.
I'd love to go again, these days. Maybe for CBB, though as regular BB is depressing. Although standing outside in the freezing cold.
The crowds would be a major put-off these days. Them booing in your ears, every time a housemate's name is called out.