I recently played South of Midnight, which is one of the best games I've played in years. I'm really surprised it didn't get more attention. I think it has the best sound design of any game I've ever played and beautiful art and story throughout.

It uses a stop motion style for character animations, which is pretty close to low frame rate, I'd estimate around 15fps (at least the way it was implemented there). I have to say it was the one part of the game that I disliked. I could see the purpose, I could see that it fit well with the general art direction. I just found it very uncomfortable and tiring to look at after a while. Fortunately they were smart enough to acknowledge this with a menu setting to disable it.

If you do decide to artistically lock your game to a low frame rate, please do your players a favor and allow them to unlock it.