Lenstip tested the Sony 20mm G and concluded:

I have to admit I didn’t expect to be charmed by the performance of the Sony FE 20 mm f/1.8G. Still, I had an opportunity to check out that lens not only during a studio session and my traditional session outside but also during a week-long trip to Iceland and it performed wonderfully well (several sample shots from that trip I post below). The lens is small, lightweight, handy, but it allows you to use ordinary filters with a diameter of 67 mm, a really moderate value for this angle of view. It’s a joy to use in landscape photography and its great aperture fastness provides additional advantages when it comes to wide angle astrophotography.
In fact, the lens has just one flaw, something you could anticipate and expect. After all it would be foolish to think an instrument with such dimensions and parameters would be able to correct vignetting in a perfect way. Well, all I have to say the final result of this testing category still was lower than our expectations so it wasn’t a complete disaster.
Taking it all into account I award the Sony FE 20 mm f/1.8G our Editor’s Choice badge without any qualms. The lens deserves it.

Sony 20mm f/1.8 FE G:
In USA at BHphoto, Amazon, Adorama. FocusCamera.
In EU at Amazon DE, Calumet DE. Amazon UK. Parkcameras UK. Amazon FR. Amazon IT. Amazon ES.

Sony 14mm f/1.8 GM at BHphoto, Adorama, Focuscamera, Fotokoch, Calumet DE, Park Cameras UK, Wex UK.

Opticallimits conclusion is:

The Sony FE 14mm f/1.8 GM has its flaws but within its category, it is an exceptional lens. The center performance is breathtaking and the outer image field is pretty good as well even at f/1.8 – quite an achievement. Technically, it is never really “tack sharp” in the corners (in high megapixel images) but no extreme ultra-wide angle lens is. There is a bit of field curvature so it’s best to pull the focus a little in infinity depth-of-field scenes. Image distortion is low even in raw images. Unsurprisingly, the vignetting is quite extreme at f/1.8 so it’s best to leave the image auto-correction activated. This also takes care of the moderate CAs. Positive aspects also include the smooth bokeh – unusual for such a lens – and the way sun stars are rendered at smaller aperture settings. The flare resistance is also better than usual but, of course, present when pushing it.

The Sony lens offers a very high build quality in a compact, lightweight package. The lens body is made of some compound material but it feels solid and combined with the anti-dust- and moisture sealing, the lens should be good enough for professional abuse. The AF is super fast and silent. If you prefer setting the aperture on the lens you can do so with this lens. Video makers will also appreciate the clickless option for it.

If you are an ultra-wide fanatic, the Sony FE 14mm f/1.8 GM is your ticket. Due to its fast max aperture, it is also more versatile than more conventional prime lenses in this range. And it’s reasonably priced for what it is. Highly recommended!