As luck would have it, I ended up with two Kindle Oases thanks to a sweetheart husband who ordered one for me as a surprise, not knowing I had ordered one for myself
Screen:
Oasis A: On quick glance and when immersed in reading, the screen's lighting and color is an even yellowish-white with no light cones or shadows. If I look for it, I can see a slight color shift from yellow-white to yellower-white, but it's not noticeable to me while reading.
Oasis B's screen is disappointing. Obvious light cones and shadows that are immediately apparent, and color splotches of yellow and green.
My Voyage (which I love) has even lighting, no light cones or shadows, but it does have a color shift from creamy white to pinkish white. However, the shift is gradual and even so it doesn't bother me, unlike the splotchy color on Oasis B.
With the light set at 0, the text on all 3 Kindles is equally crisp and clear. But when the light is turned on, the text on both Oases become a little washed out and foggy. It seems the light layer, when activated, has an adverse affect on clarity and contrast. The Oasis screen is still good, but when put side-by-side with the Voyage, there is a small but noticeable difference.
Overall, Oasis A has the most even lighting and color, but the Voyage has the crispest, clearest, sharpest, darkest text. I also prefer the creamy-white/pinkish-white color on the Voyage to the yellow-white on the Oases, but that's a personal preference.
Form Factor:
I love the light weight and ergonomic balance of the Oasis. I love the tiny overall size, which doesn't sacrifice screen size. Next to the Oasis, the Voyage looks clunky.
I appreciate the wedge-ledge on the Oasis that gives you a little place to rest your fingers, making the Oasis easier to hold. The assymetrical shape appeals to the quirky side of me, but I can see how it would bother those with a penchant for symmetry.
I am not a page-button person, preferring to tap the screen, but these page-turn buttons have a nice feel when pressed and I may start using them more. They are perfectly placed for people who like turning pages with a button. For me, they kind of get in the way as I haven't figured out exactly where on the bezel to rest my fingers without accidentally pushing a button. The click is also surprisingly loud.
Cover:
Both Oases have the black cover, which are oddly not the same. I'm not sure if it's just the natural variations of leather, but Oasis A's black cover is thicker with a rich, textured, leathery feel. When I see and touch it, I think "leather." Oasis B's cover is thinner, with less texture and doesn't really seem "leathery."
Also interesting, Oasis A's cover came out of the box wrapped in white tissue paper whereas Oasis B's cover was in a plastic sleeve.
While the cover protects the screen nicely, it doesn't do much for the back and sides, and I am inclined to slip it into a sleeve for extra protection.
Use:
I've only had a chance to read on the Oasis for about two hours, so I can't comment much. As far as I can tell, the software is pretty much the same as the Voyage, except the Oasis has the Amazon Ember font and the battery gauges in the quick menu show percentages for the Kindle and cover, which is nice.
Page-turns and keystroking were quick and responsive — as good as or better than the Voyage.
I read with the cover off because the ergonomics and light weight are the reason I wanted the Oasis. With the cover on, it's definitely "heavy" in my hand.
Finally, I'm not sure if this is relevant, but Oasis A came from Amazon and Oasis B came from Best Buy.
YMMV