I got a second Oasis. The lightning is a little better, but there are still more shadows on the edge than I was expecting. Mostly because the first had one extra-bright light in the upper right hand corner which is really distracting. At least the lights are of more similar brightness on the second one.
However the second one has a tiny pinhole in the text area.
I will have to read on it and see if it is distracting. Overall I'm very disappointed in the screen. It may be whiter than my Voyage, but I still think my Voyage has more uniform lightning and less shadows than either Oasis and my older Paperwhites. I was hoping for an improvement and not a step backwards in my opinion.