In both Dramas we have a strong-minded/quick-to-fight, main female lead, and a rich/bratty/stubborn/childish male lead.

The differences between those two dramas, is that in Promise Cinderella, there is a 10 years age difference between the main leads; while in Hana Yori Dango all the characters had the same age.

Excluding the age difference, everything else is the same.

Promise Cinderella it's a fun thing to watch if you want to see sth at the end of the day, but you can't take it 100% seriously.