Oh I didn't mean the first 3 weren't good for full parties, they're great games all around, especially 2 and 3. I just find that the item system in 5, 6, and 7 is a more enjoyable way to play with other people due to the fact that they can be used a lot more strategically than simply just getting an item and using it on yourself.
One thing I did forget though, is that Mario Party 6 has a few Mic minigames. They can be played with the controller but the fact that they are in might turn some people off. Personally I don't think it affects anything but just so you know.
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