When Apple started the use of Retina displays on the iPhones and iPads, the sharp screens really made the previous generations of Apple devices look outdated. The same thing happened with the launch of "Retina 5K iMac". This iMac featured a display full of pixels that's made even better by its hefty internals alongside its sophisticated aluminum body that rivals still struggle to beat.
One year after launch, the "iMac with Retina 5K" is still the only 5K monitor option that you have aside from the "Philips 5K LCD monitor". With the market still enjoying the fun of the 4K technology, it may be a while before other brands release their own 5K panels, making the "Retina 5K iMac" a great choice.
Being a future oriented tech company that Apple is, they have scrapped its non Retina iMac 27" and introduced three 5K Retina models. They still offer a non Retina iMac 21.5" though. But the three new 5K Retina iMacs have the sixth generation Intel Skylake processor and an upgraded AMD graphics. The displays also sport a wider and multimedia friendly DCI P3 colour gamut.
If there is an issue with the new iMac's body, it would include the lack of adjustability when it comes to height. If you want to use the thing at eye level, you would need to go resolve the issue caveman style, i.e. lift the machine onto a higher object like a pile of books. Overall, the star of the show is its display. The screen is very vibrant, to the point where you have to lower down the brightness by a couple levels if you are in a dark room.
Everything else is positively satisfactory. The pixel resolution is great; the icons, menus, and images are portrayed at a very detailed level as well; even the wallpapaer is very sharp. But if there is another issue with the "iMac with Retina 5K", it would be its lack of the Target Display Mode that lets you connect consoles and other devices. However, its full specs isn't so bad in any way, it's got a 3.3Ghz Intel Quad-Core Intel Core i5 processor with a 3.9 GHz Turbo Boost, OS X 10.10.3 Yosemite operating system, 8 GB memory, 27-inch (diagonal) Retina IPS display (5,120 x 2,880), graphics of AMD Radeon R9 M395 with 2GB of DDR5 memory, and weight of 21 pounds.
Pricewise, the "iMac with Retina 5K" starts at US$1,799.