... The tower climbing with the bullet bills was nice.  The moving walls were also neat.  Keep in mind that this was also a demo which needed to be pick up and play ready, and needed to show off specific things.  That level was obviously made to show off the cat suit climbing.

Anyway want to show me the big barren parts here?

http://www.youtube.com/watch?v=kYZcEnFNjRU

Virtually everything that's not in a pipe.

Aside from the bonus segment (which is no better or worse than most of those in Galaxy) there is no point in that level where you cannot get to a pipe within 3 seconds.

The level is built around pipes and was chosen for the demo to accentuate that feature.  Naturally, there are platforms to connect the pipes.  And yes, these platforms are a bit bigger than they'd be in other games to accomodate more players.  But, as I said, there is no area you'll be on for more than two seconds that is "barren".

Edit:  Please try to tell me there is more dead space in 3D World than in Beach Bowl Galaxy over here.

http://www.youtube.com/watch?v=YVlB_zNjuwc

Beach Bowl had an open level to explore though, if you're gonna be linear you need to be tight.

Don't get me wrong, I would love for 3D World to prove me wrong. I'm just not encouraged so far.

So... wait... op says Super Mario 3D World contains less obstancles than other 3D Mario games because of its multiplayer... At the same time, what we've seen of Super Mario 3D World actually more obstacles than many areas of Mario Galaxy... which you seem to admit is true... so... huh?

Edit: Lot of empty space here too. 

http://www.youtube.com/watch?v=BuO9qRbPY0o

Lol, it doesn't matter what anyone here says because anyone with a family or in a college dorm with friends who aren't nerds are going to buy this and it'll sell millions because local multiplayer Mario's do that. Dat Mario pu**y-power is coming and it's scurry.

Well at least the local multiplayer mode of this game will help to increase the sales of the WiiU...

The Galaxy games and 64 are also full of areas with lots of obstacles and objects. And areas that don't cater to a static camera that needs to show everything to four characters and never lose them.

There have been 5 levels shown in the game.  One of them was a boss fight and a good one at that.  One of them was something never seen in a Mario game before.  A third you admitted had a lot going on.  In a fourth you are no further than 3 seconds max away from something to interact with at any point. So I don't really get what you're complaining about.

Oh, and players don not need to be on screen at all time.  If a character drifts offscreen he can bubble back to the rest of the cast.  So, the camera doesn't have to show all four players and never lose them.

The grass level and the water level are too empty and the other two, while better, still feel too simple at times.

I just haven't seen an "Oh that's clever" part yet, and if I took 5 random levels from the Galaxy games I'd  see multiple such moments.