This new line of iMacs is the first to not have a built-in DVD Superdrive. If you're into video editing and want to put your project on a DVD, (which was one of the big features Apple use to tout about for the iMac) you will need to buy the external Apple Superdrive. When you need to connect external drives to your computer because of how the computer's design changed, it makes that computer that much less elegant and a lot less as easy to use.
If you are thrilled with the new design of the iMac and are dead-set on purchasing one, I strongly recommend purchasing the AppleCare extended coverage which will extend the standard one year warranty to three years total. I personally can't recommend these iMacs because of how far over-the-line Apple has taken the Design over Function philosophy.