Well, for starters, unless you use an app like SwitchResX, the MacBook Pro will always be at a resolution of 2800x1800. What OS-X does is it scales the apps to a specific resolution (one of them being 1680x1050). If you WERE to use SwitchResX, and force the resolution to 1680x1050, you will notice the display being very blurry in comparison to the standard MacBook Pro. Unless you have a very specific reason, I would not recommend using the MacBook Pro Retina at that resolution.
Now, if you were to compare the two, things start getting complicated. On the MacBook Pro Retina, certain apps, icons, etc, utilize the 2800x1800 resolution, so they will look more detailed than the standard MacBook Pro. Apps that do not support the "Retina" display will tend to look fuzzier, and perhaps
worse on the MacBook Pro Retina. However, more apps are supporting the Retina display every day.
Also, the overall display is FAR superior. The MacBook Pro Retina uses an IPS LCD (vs. the TFT LCD standard MacBook Pros use). IPS displays have better viewing angles, colour ratio, and darker blacks (the screen's maximum brightness and white levels is slightly inferior on the Retina, but you honestly don't need anything brighter). Finally, screen glare is mostly fixed, as the entire display is one layer of glass. In other words, the screen isn't "embedded' into the display, it's all one layer.
AnandTech has written a great indepth review of the MacBook Pro Retina, listing off the advantages and disadvantages of the Retina. The standard MacBook Pro does support some legacy ports, and can be upgraded in the future. But if you spec the Retina while keeping the future in mind, and have the extra cash, I would highly recommend going with the MacBook Pro Retina model.
AnandTech's review:
http://www.anandtech.com/show/6023/the-nextgen-macbook-pro-with-retina-display-review/