Pros: -Very compact and stylish on my GH2. -Awesome low-light performance wide-open at 1.7 and very sharp at all other apertures. -Great bokeh for video and photos. -No distortion. -Chromatic aberration is non-existent. -Focal length is perfect for street video/photography at a 40mm equivalent to 35mm full frame. Not too wide or telephoto. It can be used as a portrait or landscape lens. -It doesn't have the best build quality, but it is certainly very solid. -For the price, (I got mine for $296), it is a steal for the sharpness, compactness, and fastness of this lens. -A lot of fun to shoot with.
Cons: -Auto-focus is a bit on the slow side. Not as fast as the Panasonic 14mm f2.5, but it is okay for taking stills. As for video, the motor is too noisy when searching for focus and it goes in and out of focus while aimed at a subject. -Manually focusing should be used for video, but it has a learning curve. There are no exact measurements on the lens for focus racking, and on the GH2, there is a really poorly designed focus meter of how close and far you're focusing. I don't even know when I'm focusing at infinity or not! The compact size becomes a trade-off because if you were to have big hands, then racking focus can be a frustrating experience. On top of that, there is no OIS built in which forces you to be extremely delicate when manually focusing the lens handheld. However, I am already used to manually focusing on the 14mm f2.5, which is even smaller, so as long as you practice doing that, then the 20mm f1.7 should be a fun experience.
To sum things up, this lens is a must-buy for all micro 4/3 users. I have only had this lens for a few days, and I completely regret not initially getting this when I bought my GH2 earlier this year. Even though it does have a frustrating manual and auto-focus mechanic, that should not sway you from the clarity and beautiful rendered bokeh it produces. Out of all of my lenses, this tiny 20mm f1.7 outperforms every one of my legacy glass in detailed image-quality. I have no idea why I've hesitated so long to get this lens, but this has become a very enjoyable experience and it will stay on my GH2 80 percent of the time. If you are a micro 4/3 user, this needs to be in your kit NOW.