It does feel like a strong season just kinda fizzled out at the end. Decker's fate was an unsatisfying end to his arc, and it's weird that the threat from the government has just disappeared from the story. You'd think the mermaid attack on the government's boat crew would've brought the Feds out in even greater force.
It's also weird how little anyone seems to care that Xander murdered Donna. She may not have been his target, but it's hardly an accident; he intended to kill someone and a different person got killed as a result. I get that the sheriff can't publicly reveal what happened, but letting Xander walk away with a slap on the wrist hardly seems commensurate.