As I've indicated before I'm not going to go into this thoroughly until I have some decent raw development software to work with i.e. Adobe Camera Raw. However a few things are obvious even using the lens for just a day.
Firstly it is a sharp lens. Just how sharp its possible to get the files it creates I've yet to discover. Its certainly sharper than the new kit lens, though not by a huge distance, as far as I can see so far. Decent raw file conversion may prove much more definitive on this.
As you can see from the comparison above it's not a huge lens, and slightly smaller than the new kit lens when folded in. The large lens hood for the 12mm isn't available yet (Typical!) but I have one on order. However I didn't have any problem with flare yesterday.
I was really pleased to see that it performs really well at f/2.
I've always thought that the Panasonic 20mm f/1.7 was the best lens I've ever used wide open, but this is better. Really very sharp indeed.
Since its so good wide open it follows that all the other apertures should be good too, and that seems to be the case. I'll do some more testing at a later date and let you know what I discover.
To be honest, in terms of IQ its very much what I was expecting. All the reviews and samples I looked at indicated that this was going to be a top quality lens. Its certainly one of the best m4/3 has to offer and with its fast aperture and wide-angle will be very useful to many photographers. Shame it's not cheaper!