For super serious, I think SoO is really pushing the boundaries:
"TEEN
Content is generally suitable for ages 13 and up. May contain violence, suggestive themes, crude humor, minimal blood, simulated gambling and/or infrequent use of strong language.
MATURE
Content is generally suitable for ages 17 and up. May contain intense violence, blood and gore, sexual content and/or strong language."
"Suggestive Themes - Mild provocative references or materials"
http://www.esrb.org/ratings/ratings_guide.jsp
There is nothing "mild" in how provocative ("causing annoyance, anger, or another strong reaction, esp. deliberately.") child prisoners, impaled corpses, forced gladiator battles, living targets, etc, are.
I don't think it quite breaks the T for Teen boundary ... but it's right at the damn limit.