Nice topic.
The obvious ones (particularly Wildfire at Kolmarden) have been mentioned, but I'm going to throw Peppa Pig World at Paultons in there.
Before PPW, Paultons Park wasn't that well known outside of the local area and goondom. For a littel park tucked away on the south coast of England to announce a major new area with a strong IP was unexpected. Having grown up locally and knowing the park well, I never thought it would be so ambitious. Not only was the announcement unexpected, but so was the reaction to it. Families flocked from all over the country and they doubled their gate numbers. I don't think even the park themselves expected such a positive reaction. The success of PPW lead on to new rides and investment, especially the two new creds for us last year!