Here's another lens I got in a trade for some other items, and though I didn't really want it as I had other 28mm lenses, I decided to give it a go anyway as it was in close to mint condition.
To my surprise the lens was pretty good. Actually check that, it's really good. Sharpness across the frame, even wide open is very decent, and in the centre is truly excellent. Not Nikkor Macro good, but not far off. Still, that's more than plenty good for a cheap, compact wide angle.
As you stop down, the results only get better. The centre doesn't improve a ton (as it is already very good), but corner sharpness does lift a bit.
Here's a sample, with a huge crop to demonstrate how good it is wide open.