My wife is hooked on the game. However, she's been able to build a thriving Springfield without spending any real money. We're on level 18 now, so there are a sufficient amount of unlocked characters right now, so there isn't too much waiting. It's more like a virtual pet game, it's something you load up every couple of hours to check on your characters.
Personally, I think it's one of the better games that uses a free to sign on, but includes premium content if you so wish.
__________________
|