I already owned the 12-40mm and 40-150mm f/2.8 PRO lenses when I bought this lens on July 26th. I found this lens to be an on par addition to those two lenses.
I have had the opportunity to use this lens with both my E-M1 and my E-M10, and the images produced are very fine indeed. The lens performs admirably at varying apertures (I gravitate to f/2.8 to f/7.1). The colors produced are vibrant, and the images do not lack in sharpness. I also own the Zuiko 7-14mm f/4 lens, and this lens has proven thus far to handle flaring better than that lens does, though I use that lens on a different Olympus body. I will get around to testing that one on one of my OMD camera bodies.
Some are concerned about the weight of the lens. The lens has quite a set of glass under the barrel, so yes, the weight is more than that of the 12-40mm PRO, but quite a bit less than the 7-14mm f/4 lens I have owned for several years. It fits nicely on both the E-M1 and E-M10 (I have the Olympus grips on both cameras). Even at my age I have no trouble walking, or hiking about with the lens and camera in tow.
If a wide angle experience is something you seek, I can highly recommend this lens, the images will not disappoint, provided the photographer is on his or her game. This lens is a welcome addition to the m.Zuiko line up.