Took it for a test down the park yesterday... following are the initial impressions:
Centre sharpness great from wide open, although at f/1.3 it suffers from reduced contrast. This clears up from f/2.
Sharpness degrades as you go away from the centre, but this does improve a lot as you stop down. The extreme border does remain soft regrdless.
The lens exhibits blue/yellow lateral CA which is noticeable. I haven't observed any noticeable longitudinal CA so far.
Vignetting... the image circle doesn't fill the m4/3 sensor. It does expand slightly as you stop down.
The three aperture blades do give triangular bokeh which gives its own character.
As is, the lens doesn't do macro with a minimum focus distance around 40cm for not much magnification at all.
Distortion... in field conditions it seems to look like some barrel distortion at longer distances, noticeable on straight lines e.g. buildings. At close focus there was a hint of moustache. This really needs a test chart to nail.
Example of vignetting varying with aperture (also shows distortion):
100% lossless crops from camera jpegs as above, centre and top right corner of building.
f/1.3 (note this was a bit over exposed as the camera ran out of headroom)
f/8 looks like diffraction has softened the centre slightly, but stopping down helps in the corner.
And finally, some flare example. Sun was out of shot to top left corner. The lens might be helped with a suitable hood.
Because of the lack of coverage, it isn't really wider than the kit zoom at 14mm, but of course you do gain a lot of aperture should you need it. I think that is the strength of the lens.
Now for more samples, having a close look at close up performance.
This is what it looks like with the bluebells at minimum focus distance. Not really close at all with the wide angle. How's the bokeh?
We're still at f/1.3 here. It's nice and round wide open in the middle, with a bit of outline. The shape does degrade at the edges (taken from top-right). The CA also impacts here. I haven't tried correcting it yet.
If you want to do really close ups, you need external help. Here I'm using part of a two piece "wide angle adapter". One piece by itself works as a close up filter. It appears to be somewhat corrected and coated, but still may impact lens performance. This lets you get pretty close. I estimate the maximum magnification to be around 0.2x.
Another wide open sample.
Stopped down a bit (can't remember how much). Note triangular shape appearing.
Wide open. Note shallow depth of field here.
Stopped down a LOT.
I like this one personally. This was stopped down a bit as you can see from the triangular bokeh which in this shot I think adds to not detracts from the overall impact.
I think I'm going to like exploring semi-macro wide angle. The DoF fall off is much less steep than with longer focal lengths, so even slightly out of focus areas are usable. Also the wide perspective background will be interesting. I always wanted a wide angle macro, this combination is a good start to it.