Note that there is no secondary aperture number. This is a constant maximum aperture zoom lens. Even in 2012, there aren't that many of them, and they certainly haven't outnumbered typical variable maximum aperture lenses. Beyond all that, this is a first for a mirror-less system.
It will carry a premium price. Was there a doubt? US$1299.99 isn't bad considering the maximum aperture, weatherproofing, and hopefully, amazing image quality. The last is a big hope, given the small size of the lens. I expect the companion 35-100mm f/2.8 to be somewhat more expensive, given that the materials used will be larger.
On one side, the micro Four-Thirds users are complaining about the price, even though they might not need it. On the other side, the Canikon users are being somewhat indignant about the quality, the sensor size, and the Panasonic name. (it wasn't that long ago that I wasn't sure about Panasonic making cameras but since the DMC-GH2, they've convinced me.)
What comes to my mind is a comparison to Olympus' Super High Grade 14-35mm f/2.0 lens. That is one of the finest "normal" zoom lenses, ever. The price echoes that thought, also: $2299.99. I know someone has used the lens extensively and had to back off using it for portraits, as it showed too much facial detail. (It's no wonder there are variable soft-focus lenses for medium format.) I'd love to see how these two lenses compare. Of course, if it only comes to the image quality of the High Grade 14-54mm f/2.8-3.5, I'd be disappointed in such quality for the price. There is a limit to how much weight or space I want to save--for the price.
I'm really not expecting great things. Previous X-series lenses have been mediocre, no matter where they fit in micro Four-Thirds land. However, there are plenty of people who find a 10x zoom to be a great lens, and I don't want any zoom lens over 4x. If these new lenses deliver the kind of image quality Olympus' 14-35mm and 35-100mm lenses have, it should likely drive a lot more positive attention and sales to micro Four-Thirds.
It is a format that's doing quite well against the competition anyway. Panasonic's DMC-GH2 constantly seems to be making headway in video recording and with all the cine lenses available, it should be able to produce some amazing work. I don't do video, but good equipment always makes it easier. Since the GH3 is close, I should be even more impressed when it arrives. I would expect a new sensor that will also be used in their new professional recorder for higher image quality, faster throughput and processing, and the (new!, awesome! ramdom!) 4K recording that everyone is hyping.
Considering how well the Olympus E-M5 resolves images, I'd hope that it and the 12-35mm lens would be a great pair, delivering stunning results. My skepticism keeps me firmly planted in my chair--no jumping for joy. People seem to be reporting mostly good things about the E-M5 since they've been arriving. I hope it's not just euphoria. I'd like to think that people are realistic from time to time. I'm waiting for an E-M6, just as I waited for an OM-1N or an E-3 successor. I had a notion today about Pentax's new K30: it looks a lot like what I wanted in an Olympus E-1 successor. It's just too bad Olympus hadn't wasted so much money betting on the horses.
Update: I've seen preliminary reviews on the 12-35mm and 35-100mm Panasonic lenses and I'm less than impressed despite the brand fanatics' enthusiasm. Of course, they might not be any worse than the Canikon lenses. Canikon users have been paying more for less for quite a while.
Update 2: I've got the 35-100mm f/2.8 and I also have the Olympus ZD 14-35mm f/2.0 and 35-100mm f/2.0. I'm disappointed in a lot of things with the 35-100mm f/2.8 from Panasonic. It's not bad optically--it's about what I'd expect from Nikon or Canon--but the plastic and the tacky finish seem inconsistent with US$1499.99. The lens hood that isn't completely sealed from light where it meets the lens is also a letdown. So far, the performance is good. I could have hoped for a lens more like the ZD 50-200mm f/2.8-3.5, though.