I used to play it a couple of years ago, but that was before it went 3d.
There is nothing sinister about the game... it involves killing a few monsters, chatting with other players, and doing quests to build up particular skills.
There is a bit more information on
www.runevillage.com but i would say it is definately safe for 12 year olds

but one word of warning... it is *really* addictive so i hope your son doesn't have too much homework to do!!