I've been a hobbyist photographer for 20+ years & after lugging my big (but great) Nikon D800 overseas last summer, I decided that I wanted to travel light for my next trip & picked up a Sony mirrorless NEX camera. That camera came with the collapsible 16-50 zoom lens that (in my opinion) is a decent lens but I feel like it's designed for video (which it's great for).
The second Sony lens I bought was the great 35mm f/1.8 OSS, but I wanted something wider. I couldn't justify paying $1k for the Sony CZ 24/1.8 so I went with the Sony 20mm f/2.8 instead.
I completely expected to be let down by mediocre performance, but you know what? I was blown away by this tiny lens. It's waaay underrated & I couldn't be happier. I even like it better than the 16-50.
The lens is incredibly small, has snappy focus, sharp, contrasty, punchy colors. And if you turn off the in-camera anti-vignette setting, the jpeg output almost reminds me of shooting with an old 35mm film Olympus XA.
I took it (along with the 35/1.8) to the rainy Northwest of the US & performed like a little champ. It's not rainproof but I had no problems after getting caught in the rain with it (as long as I used common sense).
Also, it pairs great with the Sony 35/1.8. They both take the same filter thread & both can use the 35's lens hood(!). The focal lengths work well together for a 'walking around kit' too. You have the 20mm for the wider angle stuff, & the 35 for picking out the detail stuff.
*My only issue I had (at first) was what I thought was a little high price, but if you look at the only other APS-C mirrorless 'pancake' lens, the Fuji XF 27/2.8, you'll see that the Sony 20/2.8 is actually a bargain.