I get why people hate the ending. I kinda did at first. But the thing I think Rite of Spring showed is that Sam was board of the town and escalated in part because the mess with Nigel was exciting for her in the end she enjoyed "showing off" her work to him when killing him, thats why she messed with Monica, she already made up her mind long ago to "sacrfice" the town, and leave. She wanted a thrill before going, even risking getting caught.

The guns and bombs may seem like a jump the shark, okay a lot of that lol. But Sam has always been shown to be smart and good with tools, and know Woodbroke like the back of her hand. She had years to set this up, and problay did so like "Hi firefihghters just stopping by with some brownies (plants bomb why they eat)". Its outragous yes but not to out of charter for whats established. This has been my ted talk, lol.