Lens reviews are so annoying. We have crappy publications like PhotographyBlog and ePhotozine that rush out worthless reviews that contain literally no useful data. We have small blogs that produce slightly less-crappy reviews, but only ever provide a personal impression of the lens, which is almost useless unless we know that the person writing it has been working in photography for decades. And even then, that can cause problems of its own since photographers are notorious for being intransigent ogres when it comes to change.
So while pixel-peepers and chart-watchers are frequently lampooned by photographers, they are easily more well-founded in their analyses and criticisms than anyone who relies on some person saying that a lens is "good."
Lens Rentals is one of the least-known, but most useful, websites for lens analysis. The reason for this is that when they do a review, they test multiple examples of a lens, sometimes with wild variation between samples. This variation is what tells us to what tolerances a lens is being manufactured. Understandably, some variation is expected. Sometimes the lens mount isn't perfectly parallel. Sometimes a glass element is ever-so-slightly out of alignment. It happens.
But when a lens shows variation of nearly 100 lines on an MTF50 chart, that's cause for concern. The Panasonic holds up well. Not great. Just well. Everything is pretty good. And if the lens cost less than $1,000, pretty good would equal really great. But instead of doing that, Panasonic has priced the lens into the stratosphere. Worse still, the lens will be invariably associated with the GH3, which exists more as a videography tool than a photography tool. And with the 12-35mm well-lampooned and the 35-100mm lampooned even before its release as being useless for video, the X-lens/GH3 combo is caught between two worlds. It's not even a jack of all trades, much less a master of any.
Panasonic isn't being nearly as aggressive as it needs to be to prevent becoming another Sharp. To me, variance of this level, tear-downs revealing internals to be mostly cheap plastic, and extremely high prices indicates a company that is not yet ready to play in the same field as the big boys. It's unfortunate that Olympus is corrupt and incompetent, because they have proven an ability to run with the big boys.