According to Dr. Raymond Soneira, president of DisplayMate Technologies, the iPad 2's display (which has been criticized for being similar to the original's) is almost identical in performance to the iPhone 4's beautiful Retina display.
Of course the iPad 2 has a much larger screen, so it has a lower pixel density of 132 ppi while the iPhone 4's display is a sharp 326 ppi.
According to the report, Apple could probably fix pixelization on the iPad 2 with firmware update that improves the anti-aliasing.
As it is, it's reported that the iPad 2 already has a high-quality display, so it isn't out of the realm of possibility for it to use anti-aliasing to smooth out edges and reduce pixel visibility onscreen.
They also mention that the auto-brightness of the device (as well as all mobile devices with the feature) poorly implement the technology. As some may know, the brightness sensor in these devices works by picking up ambient light and judging brightness based on that. The only problem with this is that it only picks up ambient light when you first wake the device. After that, if lighting conditions change, the screen remains at the same brightness.
It's an interesting (But long) read. You can check it out at DisplayMate: Link.