One of the most disappointing things about the reveal of Mario 3D World at E3 wasn't the plain graphics and music, but how barren, straightforward and simplistic the levels were. Gone were the inventive twists and clever puzzles the series is known for, replaced by levels that looked almost auto-generated.

At first (well, second, after I got done putting a hit out on Koichi Hayashida) I just thought they'd rushed it out to fill the Wii U's barren software schedule, and hadn't taken the time to handcraft each level well.

Later, however, I realized that the simplistic levels were actually a casualty of its new focus; multplayer in 3D. In order to keep all players in the screen and give each of them a good view of the environment, the worlds pretty much had to be one-sided and simplistic; if you had too may obstacles they'd obscure players and the features each one might need to see.

In their rush to try to "3D-ize" NSMBW/U's 4-player mayhem, Nintendo let it ruin the main draw of 3D Mario; its genius 3D Worlds. (Oh, the irony)

We sure have seen like a whole 3 levels

Why dont u take a good look at urself in the mirror

Im pretty sure Miyamoto said the 3D Land/World series is a completely new series, different from the NSMB and Galaxy series which will both continue as well. So now we have 2D, 3D and Galaxy series, nothing this game does will affect the "proper" 3D Mario games.

5 full ones, and snippets of others in the developer direct.

I just want my proper 3D Mario alright.... why Miyamoto.....WHY

As far as I know, Miyamoto isn't making this; he was doing Pikmin , now he's working on his new IP.

3D World is being produced by Yoshiaki Koizumi and directed by Koichi Hayashida.

Are people still not getting it?

3D Mario is now going to be split up in a multiplayer and singleplayer version. This version can't be ruined by multiplayer since that's the entire focus. That's the point.

"Please understand..."

Do we have any real guarantee they will continue with  single player Mario 3D though, or will they throw that in the trash in favour of this NSMBified laziness?

Yes, Money and sales. There is a very, very small change that Nintendo would ignore a 10 million seller like 3D Mario Singleplayer in their current state.