A 3D mario like Galaxy won't be a system seller. Heck Super Mario Galaxy did like 10 million while New Super Mario bros Wii did like 24 million.
A proper 2D mario has better chances to be a "system seller". A proper one of course, New Super Mario Bros U is good but it could have been WAY better.
I'm pretty sure that a proper 3D Mario/Zelda U/Metroid announcement altogether can pull some units with the core gamers. In fact, part of the early Wii success was because this. We already know about MK and SSB, and adding those 3 announcements will make some people buy it.
And 10M is, right now, almost an impossible number for 3DWorld.
For the second part, I agree. NSMBU can have the best gameplay, but it is too similar to NSMBWii.
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