So this game has changed drastically in the past few years, and most other reviews don't seem to reflect this. I will address some of the changes that have occurred in this game compared to what's been reviewed before.
Messages: The game has developed a storyline through quests, as opposed to other MMOs that use quests as primarily "fetch X item or kill X creatures," instead opting for dialogue, puzzles, and combat to portray a story. The plot revolves on (spoilers following) a human (your character) becoming a being known as the World Guardian when a god dies and grants them the power and task to protect the world from the return of other gods, in a polytheistic universe where numerous gods exist and interact with the player and game universe. Positive messages through the storylines are teamwork, patience, and determining your own destiny. The character is morally ambiguous, as the game wants players to determine their character's personality and background. There are also skills such as thieving which is trained through plundering tombs or pickpocketing.
Violence: The game has become more violent as time goes on, as the old combat style of "swing a sword at the air" has been replaced with numerous combat abilities, some of which show blood, although not gratuitously and it's cartoonish in most cases. Some characters die emotional deaths in quests, through being mauled, vaporized, death by medieval weapons, or magic. Violence is rarely gratuitous, although combat makes up a very large portion of the game. Some scenes may frighten younger teens, as some boss battles take place against giant spiders or other fantasy monsters, although it's not very realistic so most teens won't have a problem with it.
Sex: Some cosmetic outfits characters can have can be risque, although there is no nudity present in the game. References to sex can be made, as a "perk" weapons can be given allows them to talk, and they make references to spanking.
Swearing: Very little in the game itself, and the chatbox has a profanity filter that can be switched on or off.
Consumerism: As this game is ongoing, it requires money. Jagex (The publisher) makes money from merchandise, advertising space, microtransactions for cosmetic effects, and membership fees for premium accounts.
Drinking: Alcohol exists in the game, and some characters are shown to be drunks, but alcohol negatively effects character's stats.
Safety and privacy: It IS an online multiplayer game, but asking for personal information is against the game's rules, and rulebreakers are punished if reported for the offense.
Ease of play: There is a decent tutorial that gives an overview of a few of the game's 27 skills, and of combat abilities. However, many of the skills do not have tutorials. Combat is fairly straightforward. Higher-level boss fights require use of abilities, switching weapons, or quick-time events. Player vs. Player combat also exists, and can be tricky than combat against NPCs. Players opting for an additional challenge can choose between "ironman" mode, where all resources must be gathered manually and not traded for, or "hardcore ironman" where the above is in effect, but players only have one life, and if they die in-game, their account is locked.
Time: This game requires a heavy amount of time. To reach the maximum level, hundreds of hours of gameplay are needed. To reach "completionist" status, even more than that is required.
Support: There is a very active community around this game, and players can get support through the game forums, reddit page, or wiki site. The community is very diverse, with players who are mean to others for amusement, to players who spend their time helping new players learn the game.