Poptropica is an incredibly smart game and there truly is nothing like it online. It's been running for more then 9 years, and hasn't stopped keeping it's high quality and improving once.
I started playing it in about third or maybe even second grade, it was a large fad at the time as it likely is now. Although I struggled to complete an island, I loved it to death.
It's definitely not blunt, but this game is educational in a way that it practices creative thinking and being strategic as much as it challenges the mind. You're almost forced to think outside of the box in some islands, and some of the themes for these islands are crazy amazing. Mythology Island essentially taught me about some of the Greek mythological Gods, for example.
I say 8+ mainly because of how challenging these islands are. Heck, it took me until now (I'm 13) to understand how to complete some of these islands. But now they label how difficult an island is, and as the game improves, they're adding sound and a wider screen for some islands (previously there was a large lack of sound and music because the creator wanted quick loading time for kids) and the music sounds wonderful.
I want to rave about this game for paragraphs and paragraphs because it's just so incredibly fun and smart for what it is. And it definitely helps that the main creator for the game was Jeff Kinney, the famed author of the Diary of a Wimpy Kid series. It never, ever asks for any personal information; as far as it goes with that is asking for your age, gender (so it can generate your character correctly) and optionally it may ask for a parent's (or your) email for if you forget your password. You aren't allowed to freely speak, so overall this has the safety guidelines of Club Penguin, which is okay considering that talking to other players in the community isn't the main idea of this game. The main idea is to challenge you and to cause kids to think outside the box.
-- Which I think is awesome.