Project X Zone is a crossover game so you end up with Dante from Devil May Cry fighting alongside characters from Street Fighter and Tekken. It is much more interesting if you know at least some of the characters so you can recognise the references to their story, but the gameplay is good enough to justify getting the game even if you are not familiar with the cast. The battle looks similar to other strategy games but instead of a turn-based combat you have to perform combos like in fighting games. The fight is so much fun but it can get repetitive after 20+ hours. The story is totally nonsensical and most of the chapters follow the same pattern: a bunch of characters show up somewhere, they wonder where they are and how they got there, here comes the villain(s), villains run away when you beat them.
Before buying the game, I would recommend trying the demo on eShop, and if you like it, get the full game and it should give you at least 30-40 hours of very good gameplay.
And one tip: there is no place to level up your characters in between chapters so make sure you always kill the main villain at the end so you can get the maximum amount of experience.