Catherine's an odd, yet appealing, chick. She's not part of the in-crowd, but she still gets around... to the tune of 500,000 copies sold worldwide. These numbers come from Atlus' earnings report, which boasted Catherine's sales and strong brand performance for the Persona series.
Catherine is a good example of a fresh concept performing well, and the news of strong sales will hopefully encourage more developers to come up with unique games.
To learn more about Catherine, read Nick Tan's review - he gives Catherine an A-.