Beautiful.
The reason why I started playing in 4K was, that on 27" monitor, even the UHD picture seemed a bit rough... Also, on such a big screen (I know there are bigger screens, just me sitting 40-50cm from the screen, 27" is big

) and while wearing my reading glasses, I could see so called "screen door" effect... A thin black lines between the pixels...
There was a cheaper option though - stop using my reading glasses while playing...
So, to explain what is 4K like, you need first to understand why I went that route...
In order to show you the difference, I have made a couple of screenshots and tried to put them next to each other, but you need to take the result with a grain of salt - inn these pictures, you will not see a true representation of the different resolutions, I just switched my video output to UHD and FHD and took screenshots... The system is trying to utilize the abundance of pixels on the monitor and smoothens the rough edges a bit... Also, you will not be able to seethe screen door effect this way...
Hopefully the differences will be visible in the following pics...
Look at the planet details...
Here look at the small details, like the circular vents on top of the cabin...
Again look at small details, like planets and stars on the radar...
One last thing: In order to keep decent framerate, I had to lower some details, so I guess if I maxed everything, it would look even better...
When everything is moving, you do not notice that much, but hen you stop and start looking around, the difference is huge...