There's very little questionable about this game. Starships blowing each other up is the extent of the violence. Bodies are never seen, nor is there any death sounds (i.e., screaming). It's very mild. Other than the violence inherent in a space RTS (including bombing planets until they are clear of the enemies colonists), there is nothing else to worry about in this game. No language, sex, drinking, etc. As far as modern games go, this is one of the cleanest.
The game itself is very fun, as well. A strategic game that keeps you involved and thinking. The one caveat is that it can take a very long time to play a match. A very, very, VERY long time. Depending on the size of the map and the number of players, this can be an hour to quite a few hours. (It can really drag on near the end of a game, which is definitely a turn off - depending on your patience). Have no fear, though: you can save even multiplayer games!