Preorders: 25-50mm at BHphoto, Adorama, Amazon

Dpreview published the full review of the new lens and concluded:

With the Leica DG Vario-Summilux 25-50mm F1.7 ASPH, Panasonic has clearly focused on an unanswered gap in the Micro Four Thirds lens market. That’s no bad thing, but it does mean that this isn’t a lens for everyone, as its rather unusual focal range might suggest.
But if you find yourself in that niche – perhaps already owning the externally similar 10-25mm F1.7 and craving a bit more telephoto reach for video shooting or portrait stills – then this lens has a lot to offer.
Panasonic’s attention to detail in designing these two lenses to work hand-in-hand is both impressive and thoughtful. Not only has it given both optics the exact same body and control layout, but it has also matched the look of both lenses well where their focal ranges meet. That will mean less work for videographers both in the field, and when it comes time to get down to editing.
We already loved the earlier 10-25mm F1.7, and this lens is an extension of everything we loved about the earlier one. Like that optic, it’s a joy to shoot with whether using autofocus or pulling focus manually, and it delivers great image quality in most respects as well.
Yes, it is quite pricey, but that’s to be expected in a niche product, and doubly so in a videocentric lens like this one. And even for photographers who’ll never shoot video, it is pretty much the only game in town if you want a really fast, native portrait zoom.
Can it justify that price tag? That will depend upon what you’re shooting, but for videographers in particular, we think you’ll be thrilled with it.