I honestly think that 3D in movies and games is just a passing fad, just like it was 50 years ago.
I also honestly don't understand what Nintendo is thinking with making a portable system a 3D system. You have to hold the 3DS at a certain angle and you must remain still. I don't know how many of you have a portable system but I doubt you remain perfectly still and at a precise angle while you are playing. The entire premise of the 3DS is a gimmick grab and the $250 price tag is not justified in my opinion.
There's a fair amount of wiggle room when it comes to the 3D, and most of it is side to side movement. It's only troublesome when you're also using the gyroscope for motion control.
As for it being a gimmick, perhaps, but only in the sense that it sets itself apart from competitors. The implementation is fairly impressive and I can see folks using it every now and then. At the end of the day it's just another graphics feature, not unlike what PC hardware and new consoles are sold on. Sure, you might claim that it's also the increased processing power for gameplay elements*, but the most apparent difference each and every generation is the graphics.
*Even without the 3D, the 3DS is your standard console successor. More powerful hardware, a few new features, and (hopefully) a plethora of new games taking advantage of that.