It manages to be suspenseful, comical, political and devastating, exactly when it's supposed to be, and that makes it more than just a monster movie. Where others would concentrate on action and CGI overdose, this one successfully presents a consequences that one unnatural event would have on society and lives of individuals. And, without being pretentious, it's a spectacle and heavy drama in one, both joyful and sad
The good thing with Korean films is that many of the directors are uncompromising in their narrative, and often come up with surprising, unusual, often disturbing and exciting result. 'The Host' is one of them. A monster movie / social criticism with a hint of 'Beauty and the Beast', it never takes side: the creature is horrific but not evil, the human foly and irresponsability don't make them just victims. Great!
I think 3-3.5 is about fair for this one. It's not the MOST evocative movie I've ever seen, but it does manage to evoke more than the sum of its parts across its plot and characters. It's a movie that firmly believes individual human voices, especially the outcasts, shouldn't be marginalized by institutions, so from a broad audience standpoint it's fairly easy to get behind.