Basic plot: The princess of Heaven has been forced into an arranged marriage with the King of Hell. She doesn't like this, and so runs away to Earth and lives there as a boy. Both the agents of heaven and hell are looking for her, but political factions within each make the search more complex than it should be. Hilarity ensues!
The best possible comparison for the feel of the series would be Shakespeare's A Midsummer Night's Dream. So much of the humour is based around assumptions, suprises, mistaken identities and people being hot for each other, and it really works well.
The books also gleefully break the fourth wall repeatedly (such as characters reasoning about what the author would probably have in store). While following 'shoujo' conventions somewhat it also openly mocks them in the storyline.
Oh, and it has one of the best comic characters I've seen in a very long time - Bi-Wal.
Spoiler.
I'm only up to Book 4 so far, but it's very very good. BUY IT.