I Got this computer mainly for my wife, but I have enjoyed using it as well. I was origonally weary about purchasing an iMac. My wife only uses Apple products, so I know the quality of the build. The reason I was weary is because the hardware is often behind the curve, at least for the price point where apple computers are normally at. Once I got to researching this new iMac, I was throughly surprised by it.
Comparing the internals of this machine to other all-in-ones, I was surprised by how good it is, and a 27 inch 5k monitor will run you around $1200 alone. That is what sold me on this new iMac. Apple did a great job when they upgraded the internals to the newest generation (7th) of intel processors, and a 4gb graphics card, makes this all-in-one a great machine, and well worth the price, when you consider the screen.
My wife mostly uses the computer for Netflix, and other streaming services, email, and a little bit of photo editing. This machine handles it all well, to tell the truth, this computer is a little under utilized with what she does, but we wanted the 27 inch screen.
I have also tested some games on it, I play diablo 3, eso, and a few other games. The computer handles it well, except for some areas in eso where a lot of other players are. If you really want to use an iMac for gaming, I would recommend the next version up, it has the intel 7600K i5, vice the 7600 i5 in this version. The 7600K has benchmarks at around 8% better, and that iMac also has an 8Gb 580 vs the 4Gb 575. While this may not seem like a big deal, the 580 has a faster clock, and obviously more memory.
Another upgrade I would recommend is the RAM, I plan to put another 8Gb in this computer, but if you are using it for more intense gaming, or video editing you can put up to 64Gb in this version, and the one above it. The $1799 iMac only supports 32Gb, I believe this is due to the processor used, but I am not sure about that.
All-in-All I am very happy with this purchase, and would highly recommend the new model iMac. If you do buy it directly from apple, do not purchase the ram upgrade from apple, they charge $200 per 8Gb which is insane, you can get 32Gb of ram (2 16 Gb sticks) for around $200, search amazon or new egg, and have a total of 40Gb. If you are not familiar with computers or RAM all the 27 inch iMacs, use PC-4 19200, 2400 MHz, DDR4, 260 pin RAM according to apple's website. It is very easy to change out the ram, there is a panel on the back side of the computer that pops out, and gives you access to the ram slots.
Below are links that I have included for the benchmarks I found, as well as the technical page from apple.
i5 7600 vs i5 7600K: http://cpu.userbenchmark.com/Compare/Intel-Core-i5-7600-vs-Intel-Core-i5-7600K/3890vs3885
radeon 575 vs 580: http://gpuboss.com/gpus/Radeon-Pro-580-vs-Radeon-Pro-575
apple specs: https://www.apple.com/imac/specs/
ram changing intrusions: https://support.apple.com/en-us/HT201191