Panasonic Lumix G X Vario 35-100mm f/2.8 ASPH lens video review by David Thorpe: Center sharpness is excellent across the frame, and if you stop down a bit-or two, it will be sharp across the 35-100mm range, corner to corner.

The Panasonic Lumix GX Vario 35-100mm f2.8 ASPH Zoom Lens Review
The Panasonic Lumix GX Vario 35-100mm f2.8 ASPH Lens with GH3 Test

The lens was tested by David on a GH3 body:

I find distortion in unnoticeable right through the range, and Chromatic Aberration is minimal-its pretty much not there.
To Sum up, this is a valuable addition to the micro 4/3 photographer's armory, and for many of those, this lens paired to the 12-35mm will be all the glass that they would ever need. You'll have the equivalent of a 24mm wide angle to 200mm tele, all at a constant f/2.8 in just two small optics. Add a weather sealed body like the Olympus OM-D, or the Panasonic GH3, and the result is a very capable and versatile outfit using just 3 items of gear. In so far as it matters, its a really good looker. Focusing speed is lightning quick, especially with the firmware upgraded to the current 1.1 version. It has

excellent performance, handling and build quality-I'm struggling to find any bad points. All I can think of is tha center sharpness is not up to edge sharpness all the way through the range. The only other criticism could be the price, its way more expensive that the other micro 4/3 zooms, but this lens is unique in its field. 

Comparison: 
Selected Items
Click to close the selection preview
Compare List
Teleconverters: Click to see the selected items
Click to Compare the selected items
Flashes: Click to see the selected items
Click to Compare the selected items
Lenses: Click to see the selected items
Click to Compare the selected items
Cameras: Click to see the selected items
Click to Compare the selected items