When you take the Olympus 12-40 f2.8 lens in your hand, you immediately feel confident.
All metal, it’s solid. The Build quality is at its best. Fully weather sealed against rain, dust and frost.
It is for me one of the best all around Micro 4/3 lens ! The perfect “kit” lens with the Olympus EM1 Mk2/Mk3
OLYMPUS 12-40 F2.8:
PROS

It’s the perfect companion to the Olympus OM-D 1 & 5 cameras.
Weighting about 380 grams, it delivers an absolutely superb image at all focal lengths from full aperture. Except for 40mm where you’ll have to close to… f3.5 to get the same sharpness.
It allows you to capture close-ups easily and to adopt new perspectives thanks to a minimum distance of 9cm with a 12mm focal length and 7cm with a 40mm focal length
No AF/MF button, you simply pull the manual focus ring and you are in manual focus.
Its wide focal length range assures you of beautiful pictures, both landscape and street… I also used it in studio for portraits. The result is fantastic!

Chromatic aberrations and blur are well controlled and the vignetting is very light.
You have a programmable F-n button from the camera if needed.
CONS
To nitpick, the vignetting at 12mm
At 40mm, you have to close the aperture a little bit to get a sharp image
CONCLUSION: If there is only one left, that would be this one!
If you need a wider angle lens, take a look at the incredible Panasonic Leica 8-18mm f2.8-4
Wish to buy the Olympus 12-40 f2.8 Pro ? ( If you follow the Affiliate link, it won’t cost you anything more and it’ll help me with a little contribution from Amazon)