This game has 2 storylines from opposing sides that tie well into each other. I recommend playing the beginner side first, party because it eases you into the game (although theres still good challenge) but also because it will make the 2nd story that much better when some of the story starts getting filled in.
You control a team of mech pilots, and can determine who goes on mission, how they improve their skills and what they outfit their mechs with. There is loads of options and customisation you can do.
This is one of the better games for adults who like strategy/rpg and want less “cute”.