Imagine if Cave Story was written by George Romero and directed by Quentin Tarantino. I imagine the result would not be unlike GunGirl 2, a freeware Metroidvania. Explore a post-apocalyptic world, collect power-ups, blast the crap out of various types of zombie, and encounter ridiculous pop-culture references.
If you want a deep and engrossing story, go elsewhere. If you’re in the mood for a game whose plot can be summed up as “Zombies over there, kill they ass”, then this is a game worth trying.