Catherine,supposed to be mature,does a good way to portray itself as such;The magnificent soundtrack,made by Shoji Meguro (though,they are reprises of existing classics),really sets the creepy,yet adult and mysterious atmosphere,and while the game goes in different kind of people,it never takes itself TOO seriously;you can easily be creeped out,laughing and feel touched at the same time.
Important also to note is that the Faithful/Cheater axis is NOT a Good/Bad axis;they both have their good sides (beyond dating a hot girl) and their problems too.Katherine is a nice,understanding woman (most of the time) but she's quite the control freak;Catherine is cute yet seductive,but she gets increasingly...Unhinged and possesive with the main character.
Your choice is yours and yours to make,out of the 9 endings the game offer.

While I said that the game didn't have much in common with Persona in virtue of gameplay and atmosphere,it does tie-in with Shin Megami Tensei.The Faithful/Cheater axis is reminiscent of the Law/Chaos axis in the older games,there are more than a few references to the older games of the franchise and you can even unlock a selection of songs from the most famous SMT game (i.e Nocturne,Digital Devil Saga and Persona 3 and 4)