Here's a crash course on Nintendo game unveils:
They hit you with the bare minimum at first, enough to whet your appetite, and show you how the game plays on a basic level, without revealing any of the juicy goodness hidden beneath. Remember how the second half of 3D Land was embargoed even from mentioning in reviews? Most people consider that the best part of the game by far, and we didn't even know about it till we played the game ourselves. That's Nintendo. Slow hype buildup to a fever pitch near release date (ideally). It's working with 3D World, although they almost certainly regret leaving a bad impression at first. They should have shown just a bit more.
Here's a crash course on how most other publishers usually do game unveils:
Give you the most bombastic, over-the-top, cinematic trailer they can churn out, pretty much custom designed to ignite our hype engines, without really showing much or any gameplay, and often resorting to tricks such as target renders or using absolutely beastly spec PC visuals. The games almost always underwhelm compared to their reveals when we actually get them, but hey the pubs got their pre-orders, so why should they care, right? I think these practises are become more obviously transparent though, so they aren't working as well as they used to.