I got it for my 9 year old, and I think that's the age group it will appeal to.
I've got this on both of our DSi's. I've played it once; I lost interest after trying to set up the camera angle 'just right' and failing to do so in a most miserable fashion. My daughter, who is 9, on the other hand, has spent countless hours playing the game.
I'm giving this game a 6 because I think it does appeal to a certain age group and subset of adults. Those who enjoy watching themselves look like fools on camera will be in for a sure treat with WarioWare Snapped; and for this reason many many children will find it highly entertaining and you may find yourself forced to participate in a round of the game, just to keep said children amused with the action replay of your gaming antics (yes, it's truly humiliating).