It's fun. I've played it with my niece and my brother-in-law. It *can* get expensive, but really you only NEED 7 characters to unlock everything (one from each classification.. ) and the starter pack comes with three of them. Others can be bought in packs of two or three, I think, as well as individually.
As for your other questions:
It's fairly easy, but I didn't find it repetitive (nor did my niece, who's a better gamer than me. Haha.) There is TONS to do.
The worlds are pretty well designed, in my opinion (and that of my niece and b-i-l). The graphics are pretty rich, the voices aren't annoying. There are a lot of different places to explore and a lot of different things to kill and collect.
The characters are well designed and a lot of them have pretty neat "weapons". They also each collect their own gold for upgrades, so if you want to upgrade one, you have to use it.. which some people may not like, but I thought was kind of cool.
The toys are actually very well made (aside from a few anatomically impossible positions!). The painting is nice and detailed and they're unique.
I would definitely recommend it for kids because you can swap out the characters at will and two can play at a time. Also, it's fun! Heh.
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