Sure, the new iMacs have a couple of Thunderbolt ports and more grunt between them, but other than that has much else changed? To answer that question, we'll defer to the iFixit guys, who've already torn the 21.5-inch iMac apart.
In their teardown, they found that the PCI Express and DisplayPort both have their own 10GBps data channel so that the display and hard drive aren't competing for bandwidth. They found it pretty easy to rip apart, scoring it 7/10 (with 10 being the easiest to repair.) Check out the full teardown over here: [iFixit]