I think large parts of the ESRB's rating of the game have to do with the themes of Drug Abuse and Genocide prevalent throughout the game, but that's merely a guess. I can tell you the relevant parts of the multilayer:
- Blood and Gore. A number of the units die in less than pleasant ways. Specifically being skewered or dissolving in acid. These graphics are mostly mild and the units small
- Drugs. A couple units utilized stimulants as a resource (Marines and Marauders). While you don't see them shoot up there is a sound effect
- Violence. There is the expect warfare based violence and even the use of Nuclear weapons. If you find these sights disturbing, consider yourself warned.
While these graphics are all present, they are usually small and brief. After an hour of play chances are you'll barely notice them. Then again, those little Marines do have a tendency to explode in to gibbets...
A sample can be found here, consider yourself warned.
The official ESRB rating is
Teen for the following reasons:
Blood and Gore, Language, Suggestive Themes, Use of Alcohol and Tobacco, Violence
This is a real-time strategy game featuring armies of futuristic races in conflict with each other. Players control assorted units of humans, warrior races, and aliens through combat missions around several planets. Combat is presented from an overhead perspective: players' soldiers use machine guns, grenades, mobile tanks, lasers, and aircraft to kill enemy units. Artillery fire is depicted with realistic sound effects, including battle cries and yells from injured characters; explosions occur frequently, and can be large and detailed. Aliens and soldiers are sometimes depicted bursting into small splashes of blood; gibbing effects and small body parts can also be seen strewn on battlefields; and a few cutscenes may depict small pools of blood around characters, or alien blood spurting across the screen. The game also depicts characters smoking cigars or drinking alcohol in cutscenes. Characters use profanity such as "sh*t," "b*tch," and "a*s" in the dialogue.
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