I have been playing hl(horseland) for about six years now(i know, i know) and in my many years of experiance, I would definatly reccomend this game, but WARNING: watch out!
There are so many bad things about this game. For one thing, about 75% of the people on there don't care about you, your feelings, or your account. It is a good preparation for teens entering the real world because all the players want and care about is one thing: $money.
When you first start out, be especially cautious. People see you are a 'newbie' and will scam you and take your money/horses. Also, do not even attmept to play this game if you know nothing about html.
Don't worry you over-protective parents, there is not a big problem with sex. On occasion, advertisements will pop up on one of the chat rooms. (advertisements are posted by fellow members)
Also- and some may disagree- violence is not a huge problem either. It is impossible to slaughter horses on this game, though some players like to make-believe it.
One thing I would worry about though, is the language and attitute most players have (towards you).
Drugs, alcohol, and commercialism is not a problem I would loose sleep over.
On the other hand, the social behavior of the fellow players is extremely hostile, and though the educational value is extremely high, I would leave you with this warning: watch out! (if you need any help in the game, I run an Endurance Riding Club, and you can contact me from there)
Have Fun!