Does a standard, old school television program look great on a brand new high definition television?
In order to get the most out of a retina display ALL of the graphics/content must be designed and formatted to take advantage of the higher resolution. Otherwise, it's like watching "I Love Lucy" upscaled on a 1080p flatscreen.
I've noticed that all of the graphics in the mobile web sites I've designed for non retina displays look somewhat fuzzy on the better retina screen. There is a noticeable increase in saturation and contrast but that doesn't mask the fuzziness I'm can't stop focusing on. Conversely, the text generated by iOS looks AMAZING and is so much easier to read.
Below is an example of what I'm referring to. On the left is an image formatted for a non retina iPhone screen at 320x480 ppi. On the right is the same image formatted for a retina iPhone screen at 640x960 ppi. As you can see there is quite a bit of pixelation between the non retina screen and the retina screen,
(especially around the edges of lines or where two different colors meet). The image formatted for the retina screen looks great while the image formatted for the non retina screen looks pretty bad, just like watching "I Love Lucy" on a HD television would look bad.
(These images were grabbed directly from the iPhone 4s via the screen capture function. I did scale them down in Photoshop for demonstration purposes.)
In addition to the visual quality the non retina image weighs in at 129 KB while the retina image tips the scales at 443 KB
(saved in photoshop at 95% jpeg compression). That's a huge file size difference especially when taking into account AT&T's practice of throttling unlimited data users on their 3G network.
So, the answer to your question all depends on if the content is formatted for the retina display. If it is then the retina display will definitely show it's superiority. If the content was formatted for a non retina screen it will look bad. I.E. BluRay disks look great on an HD television but DVD disks, although adequate, are not at the same quality; just like the two images above illustrate.