'Watchmen' is truly a beautiful thing to behold, with Zack Snyder really outdoing himself. It's easily his best movie to date, with a complex yet fluent narrative, great performances and an different (but awesome) soundtrack. Although its running time is far too long, the last 30 minutes are touch-and-go, and the movie has to deal with arguably too many plot points, Watchmen succeeds as both an adaptation of the graphic novel and as a movie in its own right. Definitely underrated.
Although it can never fully convey the depth of the source material's world it comes darn close with an impressive attention to detail in constructing its alternate history. But it's not just surface appearances; it perfectly captures the feel of it and never shies away from the deeper aspects of its social commentary and deconstruction of the superhero. As a result we get a superhero film that explores humanity by showing the loss of it, both in the Watchmen and the cold war world.