While Metal Gear Rising: Revengeance is a very good action game, it does contain content inappropriate for some children (although not the high levels of blood gore CSM seems to think there is, we'll get to that later).
Story: In 2018, all seems well for our hero Raiden, a cyborg field agent for the "good" private military company known as Maverick Inc. He has successfully stopped a war in an African nation (although it admittedly is peace through superior firepower, a "one sword drawn keeps another in its sheathe" philosophy). However, rival (and evil) PMC Desperado has dispatched agents Sundowner and "Jetstream" Sam, a pair of cyborg warriors, to assassinate the African prime minister. Although Raiden destroys the massive war machine sent to aid them, he is ultimately beaten by Jetstream Sam. Three months later, he has a new cybernetic body and is on the warpath against Desperado, but he soon learns their plans go far beyond what anyone could ever have suspected.
Violence: Plenty. As Raiden, you have access to a variety of High-Frequency swords, blades that crackle with colored electricity and are capable of slicing through anything. Going into Blade Mode allows you to slice apart your foes in any way you see fit, but armored opponents will require that you break their defenses first. Dismembered parts will be cauterized lightsaber-style, however, and while some opponents bleed, it is a small amount that temporarily stains the environment. You also have access to a variety of other melee weapons that are unlocked after certain bosses are defeated, such as a staff made of the arms of broken droids or a pair of oversized machetes that are connected like pincers. Rocket launchers and grenades can be found throughout the game, as well. You also have access to Ripper Mode, which can slice apart foes without entering blade mode (as this is the "dark side" of Raiden, attack animations will be red instead of blue while this is engaged, and for the mission where you are locked into it for the duration of a boss fight, dialogue will make it clear Raiden has gone somewhat insane). Finally, boss finishing moves can be violent (freezing one and slicing her into pieces, throwing a flying robot into a helicopter to slice a villain into countless pieces as he falls, etc). The final boss deserves special mention, as you impale him on your sword, pull the blade out, slice away at his heart, and then rip it out. Note that the heart does not appear even remotely human, but there is blood.
Sex: No reference to actual sexy stuff, but Mistral, a boss in one of the earlier missions, is a rather "overdone" female boss. She seductively removes her jacket before the start of the fight, and although she is a cyborg, her chest moves with every step she takes. Her unique ability is having robotic arms attach to her back, which touch her in private locations in her idle stance. She also groans in a rather suggestive way while the arms are being attached to her. Additionally, Courtney (a Maverick employee who you can talk to throughout the game) wears a very low-cut shirt.
Language: Heavy use of this in cutscenes and boss battles. Mistral, Sundowner, and Metal Gear Excelsius all have at least one line with f--k in it. The final boss is extremely course in language, making use of phrases like "You little f--k!" and "Die, you piece of s--t!" One of his speeches during a cutscene involves at leats six usages of the word f--k.
Educational potential: You can have conversations with your colleagues over the Codec, and most contain accurate facts relevant to your mission (i.e: a mission set in Mexico spurs discussion of traditional Mexican cuisine, or the unique architecture of the city you are in at the time). Beyond this, not much there education-wise. Then again, if you are looking for education, the Metal Gear franchise might not be your best bet.
Scariness: A main plot-point involves an evil corporation extracting brains from children and using virtual reality training to make them into cyborg soldiers. These brains can be seen in metal casing with eyes attached. A villain picks one up during a conversation, and it can be seen squirming n terror. During on segment, you are forced to destroy a group of cyborgs while listening to their thoughts (i.e: "What will my family say when they see me like this?" "What was I thinking, signing up for this job?" "Please, God, don't let me die like this."). Hearing this while slicing them into pieces can be as stressful for you as it is for the main character (he appears physically injured and cannot fight beyond clumsy swipes that knock opponents back.) The final bosses physical appearance could be disturbing to some.
Other concerns: The last boss battle (a muscular, seemingly invincible American politician versus a smaller cyborg armed with traditional weapons) is very symbolic of America vs. Japan. The entire final battle equips you with a red sword, as well, with red being an iconic color of Communism. Parents with a problem with this should be advised. Additionally, you must break into Denver during one mission, which has been taken over by a corrupt police force. Even though they are evil, you are still cutting down policemen, raiding a corporate building, and generally breaking the law.
Role Models/Messages: Raiden wants nothing more than to save children from becoming child soldiers like he was. However, this point is muddled, as he cuts down thousands of soldiers over the course of the game. There is, however, a strong message of standing up for what you believe is right, whatever the odds.
In conclusion, this is a very fun game with a massive "cool factor", but it is still not advisable for younger children to play this.