Probably best for kids between 8-12.
My kids discovered this site a few months back. I made a quick check to make certain there were obvious spam attacks or inappropriate content, and I found none, so I let them play with the promise that I'd have to come back to dig a little deeper later.
Once I started, I found myself sucked into the game for more than a week before I could pry myself away.
Poptropica is a platformer/puzzler. The conceit behind the game is that you travel to different islands, each of which feature a different adventure. Themes include everything from history and time travel to world cultures to wacky mad scientists. Genres stretch from mystery to sci-fi and fantasy.
This is mainly a single-player game. There are a few mini-games that you can play with other players, but those are easily avoided if you prefer to focus on the larger campaigns.
This game is light in tone, but some of the puzzles will be at least a little challenging to adults.
And one of the best parts about Poptropica is that it is currently being supported. There's a team constantly developing new islands, and they give previews to new islands through the blog. Compare that to many kid-oriented sites that the creators just seem to abandon and forget to turn out the lights.
Now, some drawbacks: Yes there is sometimes advertising in the frame around the game window, and certain islands have corporate sponsorship. But from what I've seen so far, those ads are always in the background and never impact the story.
And this is definitely a puzzle game first and an educational tool second. Most worlds are based around some sort of educational goal (history, culture, art), but the factoids kids might learn are incidental to the game play.
Since there is absolutely no sound in the game, you do need to be a pretty secure reader in order to understand the rules and goals of each game. Otherwise, younger players will just find themselves clicking about randomly.
And it is a bandwidth hog. If you're running an older machine, this game will make it slow to a crawl, which will definitely impact some of the more action-oriented puzzles.
Two responses to other reviews I've seen here. I've played through all the worlds available for free at the time, and I saw nothing referring to the Christian creation story. On the other hand, Poptropica rotates in new adventures every few weeks, so that particular island may have been removed.
And anyone who thinks they're not allowed to save their game hasn't seen the big blue button in the corner of the game screen that reads "SAVE."
Poptropica is just a diversion, really. It's not as involved or violent as World of Warcraft or another MMO, but kids who are too advanced or not advanced enough may become bored quickly. Perhaps the biggest benefit of the game is that you can introduce some deeper discussions about the islands' various themes, to see if your child has developed an interest in them worth furthering.