More expensive games, longer dev cycles, less actual game. I think these issues wil plague each console maker this gen. It plagued them during the 7th gen, but I think it will be more pronounced this gen.

I beat 3D Land in about 5hours, just played through the game quite casually. To beat it 100% it took me 21hours.

I think 3D World will be the same, it will keep you busy for a while if you want to beat it 100%.

Does it really matter that it's only 8 hours long if that's 8 good/great hours? A game should only be as long as it needs to be.

A game is as long as you want it to be ;)

Let´s not jump to conclusions here, as others have seid: The galaxys, 64 and sunifshine are around the same lenght if you just rush through them.

http://gamrconnect.vgchartz.com/thread.php?id=171749&page=1#
i already posted that, he stated that it is not over after that similar to how 3D Land wasn't over after the finishing and that this run time doesn't include commander toad levels and what not

The multiplayer seems to be the important thing here (that's why there are four playable characters) so I don't think the length of the single player mode is so important but the lack of difficulty doesn't sound too good.

Yeah this is pretty common. If you breeze through it and do not care for the extras it would take around this time. It's probably around 25 hours to do everything, depending on skill.

I don't really comprehend the meaning of this.  How can you rush through a platformer.  Sure the person might have not went through stages repeatedly to get every single hidden coin, but again, it's a platformer.  That's the same thing as saying that someone rushed through a third person shooter and a first person shooter.

Uncharted 3 is only six hours long(or eight?,) but unless you collected all 100 treasures you rushed through it? 

Resident Evil 5 is, well, I have no idea, but if you didn't shoot every single hidden medal, then you rushed through it?

This isn't an RPG, or like Grand Theft Auto where the time can actually be longer than given because there are side quests and left over missions.  If all that's left over at the end of the game is to go around and pick up collectables, that's hardly an excuse to say someone rushed.  Assassin's Creed has a lot of useless collectables where you're going to one spot to collect them all.  I'm not going to count that as any meaningful experience.  Infamous and Infamous 2 has blast shards that you can collect all over the map.  I wouldn't count those either, although I would count the  side missions that you can do. 

Have you ever even played a 3D Mario game? 

From objective to objective, the level layouts and/or paths change. Sometimes even the gameplay changes. Making the levels almost entirely different ones. It's not like looking for that little oscure corner of a level while exploring like in most third person games. ¬_¬