I've sung Michael Shannon's praises a few times before here, notably in Take Shelter and Boardwalk Empire. I might not have noticed this movie if not for his name; sure it's a pretty neat story, but it hasn't been advertised very well at all as far as I'm aware, which is a shame. Shannon's performance here is just as monolithic (to reuse the term) as in Boardwalk. The characters aren't the same, but there are enough similarities in their temperaments to make him perfect for the role.
The Iceman is based on the true story of Richard Kuklinski, a man who killed somewhere around 100 people from the 1950s to the 80s. He started out killing for the fun of it and later joined the mafia as a hit-man. The latter period is the focus of this film. Kuklinski had a wife and children who never knew he was a killer until his arrest in 1986. The film paints his family life in a way that makes you almost empathize with him; he seems kind, and expresses the fact that they are all he cares about several times. Outside of the home though, killing is like breathing to him. He's not a moralistic killer aside from his "no women, no children" rule. He kills who he's told to kill, who he needs to kill to protect himself, and those who just annoy him or happen to be in the wrong place.
So, he's a pretty terrible person. The film and Michael Shannon's excellent performance take this dark spot of humanity and turn him into something less than a monster, which is probably bad in the grand scheme of things, but even an anti-hero has to be a little relatable in order for a story to work.
Aside from Shannon, we get some great stuff from the frequently more elusive Winona Ryder, gangster stand-by Ray Liotta, and a completely unrecognizable Chris Evans as the scummy ice-cream truck murderer Mr. Freezy (apparently called Mr. Softee in real life). James Franco also makes a short but very effective appearance as one of Kuklinski's more unfortunate victims.
It's a darn good movie. It's a pleasure to watch Shannon's appearance change through the decades, while maintaining his stone-cold posture and hints of inner turmoil. I hope he's used right in The Man of Steel.