This is the best STAR TREK film yet. Violence is the only issue, really, outside of some brief "d**n"s and "hells". People are shot with lasers, and many bodies are seen dead, with blood on them. Wounds range from a few cuts to one man who has half of his face bloodied up and darkened. There's a creepy scene where worm-type creatures crawl into mens' ears and take possession of their minds.
Looking back, I liked the first movie, but I LOVED this one! It does have a lot more action and is probably a good idea to fastforward through the worm-going-in-the-ear thing for younger viewers (need to get a Q-tip now, just thinking about it), but for values, this is the best movie. It talks a lot about friendship, loyalty and sacrifice. There's also a lot that can be discussed about family interactions (Kirk has a son we knew nothing about), and how science can be twisted for military purposes. There are numerous references to the works of William Shakespeare. This is one of the movies that I will always stop to watch.
Parents need to know that the second and third Star Trek movies are a lot more violent then Star Trek: The Motion Picture. In one scene, alien worms are put in the ears of two characters as a type of mind-control. Later, one of them vaporizes himself, and another bleeds a lot from his ear. Several bodies are found with blood on their faces. In another scene, Scotty carries a wounded engineer to the bridge. His face is burned and bleeding, and he dies after they take him to sickbay. After a space-battle, the main villain is seen with a bloody burn on most of his face. And the language is way too excessive for a PG movie.