Not mentioning any new titles here! FFXII's gambit system is one of my favorites, along with FFX-2. I really enjoyed the flow to FFXIII's battle system, especially when you had to quickly flick back and forth between paradigms (ie everyone needs to be on defence to survive a hit), the rhythm was so distinct. Dear god did I loathe the story, but FFXIII:LR's battle system was fantastic, and built on what XIII/XIII-2 had established but gave you direct control. For non-FF, Bravely Default was extremely creative and flexible. Of the SMT games, I've only played IV, but goddamn, the press turn system was an addictive and tense gameplay epiphany. P5 perfected the Persona formula, too.
...that wasn't a short answer.