I didn't quite understand that

example 1

British English:
The carnival was quite fun this year.

American English translation:
The carnival was decent. Nothing to write home about. Even the jerk chicken was just mediocre. It was no 2002.

example 2

British English:
The carnival this year was actually quite good.

American English translation:
The carnival this year was the best thing ever. The jerk chicken was the dog's [er/uk: that's a good thing].

Got a taste of the carnival last night and I'm definitely going back for more today. It was pretty rowdy and good fun (and then again, it was "children's day").

Here's the definitive history as explained to me by my Irish friend Rick O'Pedia if you're interested: Notting Hill Carnival.