I am friends with someone who was pretty involved in that big wave of stereo madness and 3D conversion years ago. There is huge range in quality for stereo conversion depending on how much the director cares and the studio is willing to spend.

Fun fact, Clash of the Titans (2010) was such a shitty, low budget conversion that "release the kraken" was an industry term for, "this is a shit, rushed, cheap job." There's a lot of variables unique to stereo filming and most directors don't understand it or care. For awhile many studios were just trying to cash in on the fad. Bad conversions can, at best, mean it looks like paper cutout shit and, at worst, give people headaches and make them sick.

Guillermo del Toro really cares. "Pacific Rim" is considered a very well done conversion. They even did things in the conversion that you couldn't do with a typical dual camera setup, like warping the depth offset to exaggerate the height of the robots (sort of like forced perspective, but with depth). You have to be very careful with interocular distance, convergence, depth of field, and keeping things consistent from shot-to-shot so people's eye muscles aren't screaming after 10 minutes.

I was honestly never into 3D, but I don't doubt him when he says its a good job. He was probably actually in dailies. There's as much directing that can (and should) go into stereo as any other sort of shot design.