The title is the TLDR, but in long, I'm playing through Stick of Truth and am greatly enjoying the timing/turn based combat system. The wiki notes that Costume Quest (which I own, and intend to check out once I'm done with South Park) and Paper Mario both have similar systems, but I'm looking for something a touch deeper mechanically and more serious in tone, if such a game exists. I would greatly appreciate some recommendations!

If it helps, the platforms I have access to are PC, 360, DS and PSP, though getting access to older consoles via borrowed hardware or emulation isn't a particularly difficult task.

Shadow Hearts... kinda. It has this wheel thing in which you gotta time button presses to have moves come out effectively. Super Mario RPG's system is closer to South Park IIRC.

I can't think of many that aren't Mario RPG games. I was going to mention Shadow Hearts, but @thunderslash got there first. Lightning Returns has some timing-based elements, but the combat is more active than turn-based.

Sonic: The Dark Brotherhood had timing minigames for all the special attacks. There's also Final Fantasy Theatrhythm which is basically Elite Beat Agents if it was a RPG that was also a rhythm game.

I can only think of the Mario & Luigi RPG's