This is my go-to lens for every day use, I use it for street photography, food and some portraits on my G85. Wide open at f/2.8 quality is very good and gets even better and sharper around f/4.0.
It is a decently fast professional level lens, with the advantage of nano-surface coating (which reduces flare and allows for a clearer image), weather-sealing and Panasonic's new Dual IS 2 system.
Unlike the Olympus 12-40mm f/2.8 PRO which sports a very handy manual focus clutch, distance scale and metal construction, this lens has a high grade plastic casing, is fairly bare, with no distance markings for manual focus (there is a button to disable or enable Power OIS).
Although the Olympus has a 5mm focal length advantage, you'll be hard pressed to find a better performing light, sharp and very portable lens, with the equivalent focus distance of a 24-70mm on a 35mm full frame camera.