My Take
It's the best game right now. That being said, it is a game. You can make it educational, but you have to limit the students and give them specific rules and tasks.
How I Use It
It is a good tool for anything spacial like geometry especially anything with blocks. You can also use it for its sandbox quality - creativity.
I've had kindergartners play it and love it, but the iPad Pocket Edition app is easier for them. Boys LOVE it, but girls do love it too.