Petapixel tested the OM-1 and concluded:

Should You Buy It?
Absolutely, yes. If you’re a sports or wildlife photographer, the combination of speed, durability, and the diminutive size of the lens (compared to APS-C or full-frame) makes the OM Digital Solutions OM System OM-1 one of the best cameras on the market. If you do slower work, like landscapes, and already have one of the more recent E-M1 models, you may want to wait to see what OM Digital comes up with next.

OM-1 at BHphoto, Adorama, Amazon. GetOlympus.
OM-1 in EU at Calumet DE. Fotokoch DE. FotoErhardt DE. Wex UK. Olympus DE, Olympus UK, Olympus FR, Olympus IT, Olympus ES. Olympus NL. Olympus BE. Olympus AT. Olympus CH.

The new lens is now in Stock at BHphoto, Adorama, Amazon.

ThePhoBlographer concludes:

The Panasonic Leica 25-50mm f1.7 lens is exactly what the Micro Four Thirds system needs. While the lens is heavier and pricier than most other lenses for this system, the mixture of sharp subjects and smooth backgrounds will be worth the investment for many photographers. It’s a great option for several different types of shoots, including portraits and events.

While this lens is excellent, it is an investment. Hopefully, the Leica in the name will help the lens retain more of its value if resold down the road. It’s also heavier, though not terribly so. If you pixel peep, you might notice some very occasional chromatic aberration and soap bubble bokeh. And, for Olympus shooters, that aperture ring is just dead weight.

The Panasonic Leica 25-50mm f1.7 delivers a mix of sharpness, bokeh, and versatility that make it a go-to lens for photographers lucky enough to have the budget for it. It’s a lens I would have on my wish list if I shot Panasonic; there would be some hesitation for Olympus because of the lack of aperture ring compatibility in such a pricey lens. I’m giving this lens five out of five stars.