Ming Thein reviewed the Olympus 12-100mm lens. This is his conclusion:
I too found this lens to be excellent – the one lens for M4/3. It is an impressive performer throughout the range, and has a better out of focus rendition than the 12-40 that preceded it. This property, combined with the dual stabiliser, makes it ideal for handheld video work. I have to agree with Robin that if you had to have only one lens for the system – and perhaps to cover everything – this would be it. There are very, very few compromises, and I never once felt any of them were optical. The only problem is the size: it’s very un-Micro Four Thirds, and combined with an E-M1.2 body (for best balance and full dual IS functionality) – it’s nearly the same volume and weight as an X1D and 45mm. I suppose when you consider the effective range (24-200) and relatively fast constant aperture (4) – that changes things a bit. Scalpel or Swiss Army knife? Down to individual preference, I think. The trickier question is whether within the same M4/3 universe you’d be better served by a few faster primes at similar cost; I think this is a tricky one to answer and depends on how often you shoot in low light or inclement weather situations (the primes are not as well sealed as this 12-200). Still merits a recommended rating from me.
Check out his full review at blog.mingthein.com