This was a lot more straight forward than I was hoping for, and almost embarrassingly easy. Mostly rating 3 because it has potential and a half decent story, but even the final boss is easy street if you put the pushable rock between you and him and swing away. Same with the mech bosses if you shoot them at an uneven elevation.
Not at all. Lethal is still in the underworld where Gradius (or however you spell his name) was during LRU Empires and Fatal probably somehow left that orb behind when we beat him in LRU 3, which is definitely before this game (otherwise, how'd Lethal end up in the underworld *again* in the first place?). Lethal is still Lethal and Fatal is still Fatal, it's just that Fatal was dead and using the orb unintentionally revived him.