It's probably the weakest of the three DS games, especially as it went so hard on the asset reuse throughout that it had a major impact on the whole game feeling fresh without really doing that much with the setting to make it stand apart from other castles, but there were three things that I think it did exceptionally well:
1. Insane build variety with all the subweapons and spells meant that you could experiment forever and still find unique setups to blow the game apart.
2. Charlotte and Jonathan are a really fun pair of protagonists with enjoyable banter that makes for a big departure from the normal cast dynamic that helps make the game stand out on that element alone, if nothing else.
3. The final boss fight, even as obvious as it was going to be based on how the game plays, is legitimately my favorite final boss fight in the entire series. Really fun patterns to learn and the whole concept is executed so well throughout.
I feel like if it had a bit more time in the oven and a better character artist for the portraits (tee hee), I think it would have easily stood side-by-side with Dawn and Order. The bonus modes are all mint, though!