If you were looking for a redesigned iMac or perhaps one with a higher resolution display, then this isn't your upgrade. The new iMacs look exactly like the old iMacs, with the upgrades all coming on the inside. Apart from the shift to quad core Haswell processors, it also gets improved graphics. The entry-level 21.5" model shifts from Nvidia graphics to Intel Iris Pro GPU, while the other models jump to newer Nvidia graphics cards.
The new models also make the leap to 802.11ac Wi-Fi. It can deliver cutting-edge wireless speeds, but only if you have a router that also supports 802.11ac (and your internet connection speed will also limit anything but local networking).
The late 2013 iMacs also give you some improvements to the pay-to-order Fusion Drive and all-Flash storage options. Apple says that switching to PCIe-based flash storage will make both of those options up to 50 percent faster than the same options on last year's model.
The new iMacs are still shipping with Mac OS X 10.8 Mountain Lion. Apple's upcoming update, Mac OS X 10.9 Mavericks, should land by the end of the year. We wouldn't be surprised to see some Haswell-refreshed MacBook Pros launching alongside that big software update.
Pricing is the same as last year's models were, starting at US$1,300 for the base 21.5" 2.7 GHz model, and moving on up from there.