Addendum said:
Animal Crossing? Nope. I don't have a Gamecube.
The Sims? No, though I have played SimCity.
Pikmin? I don't have a Gamecube.
Hmm...well, this is a totally invalid comparison probably, but I'll make it anyways. You know how in Simcity, you would start with just this ruined patch of dirt and you'd add buildings and more people would come in and you'd have more tax revenue to build better things for more people and how you'd have to build things based on the demands of the people already there? Viva Pinata will sort of be like that.
You start in an almost-desert with just patches of dead grass and ruins around, and you go from there, you just build a garden to attract more and different species, just like you would build your city in SimCity to attract people, but it's a little more complex than that. Certain Pinata's just don't like each other and will fight over resources, some of them will mate and create whole new breeds that might threaten your other stuff, etc. You can also attract "bad pinata's" (I don't know what their actual name is, the red looking evil thing in one of the screenshots I posted is an example though) which will also eat up your resources and other pinata's, which I guess would be comparable to natural disasters in Simcity.
You have to be more creative with ways to get rid of them though, because if you take the direct approach and just cross breed some doomsday pinata to go and kick it's ass, it'll burst and it's candy will go everywhere, and any pinata that eats it has a small chance of going "bad" and causing your problem to just get bigger.
There's also an online enconomy thing with it, with you being able to mail a box back and forth with a friend containing several pinata's. For example, if my friend has a problem with bad pinata's, and I have a problem with...something, I don't know, I could mail him a breed of doomsday pinata's that I've created in exchange for him mailing me the building plans for something new, or a new breed, something like that.
That's a really loose comparison, and there's more to the game than that, but yeah, if you liked Simcity/ever play and like Animal Crossing, you'll like Viva Pinata. You can probably find better info
here, if you want it.