There are few things I enjoy more than Roger Ebert raging about 3D. Case in point:

But “Titanic” was not shot for 3D, and just as you cannot gild a pig, you cannot make 2D into 3D. What you can do, and he tries to do it well, is find certain scenes that you can present as having planes of focus in foreground, middle and distance. So what? Did you miss any dimensions the first time you saw “Titanic?” No matter how long Cameron took to do it, no matter how much he spent, this is retrofitted 2D. Case closed.

Oh, but there’s more to it than that. 3D causes a noticeable loss in the brightness coming from the screen. Some say as much as 20 percent. If you saw an ordinary film dimmed that much, you might complain to the management. Here you’re supposed to be grateful you had the opportunity to pay a surcharge for this defacement.