Taking place a little while after the end of the second game, this third installment in the franchise is basically a combination of the first two with an overhauled combat system. Making it easily the best of the bunch (once you install the re-translation project to reduce the terribleness of the localization).
Character-wise, with the DLC, you get access to the whole cast and don’t have to jump through any hoops or waste any Plan space to unlock characters (although Uni, Ram, & Rom don’t become available until the last chapter). Story-wise there’s only some especially cringy moments in the 6th chapter or so. And as for the re-used assets… well, there’s still a ton of those.
The most notable improvement here over the previous games though is the revamped combat system:
Instead of having an EX Bar that the entire party has to use (and which has to be re-filled every time you enter an area), each character’s SP pool doubles as an EX Pool. Meaning now you can pull off multiple 3-bar EX attacks in a row. Even better, the game now tells you when an enemy you’re attacking happens to be weak/strong against an element and even specifies whether an attack you’re about to use is magical or physical.
Another new addition is an in-game achievement system. By doing things with each character like running, jumping, taking damage, switching in combat, using items in combat, and so forth, that character will get stat boosts and unlock character-specific Plans to further boost their stats or add new abilities (like a 5th combo slot).
Really, the only flaw with this entry (besides the localization and re-used assets) is that the DLC character Events are bugged to appear a chapter earlier than they should. So if you’re only able to get one of the three games, this would be the one to prioritize.