When people play it they're going to see it is, every bit, a "true" 3D game. People are crapping the pants and making a very big deal about nothing, going off of very little info, as per usual on internet forums.
Granted, when they first revealed it, I too felt disappointment, because it's not the epic 3D Mario that I've dreamed of since Mario 64 came out.
The major difference is, however, that I actually got the fuck over it, and now accept this game for what it is. I haven't loved EVERY Mario game that's come along (Sunshine, Galaxy 2), but I think this game in particular looks pretty damn fun, and I'm still hoping Wart and Shy Guys and Mouser, etc. are secretly somewhere in the game. They REALLY need to bring those guys back. Another straight-up jaunt to Subcon is highly called for.
