It's fantastic. If my house burned to the ground and my camera gear was a complete loss... I'd use the insurance money to go buy the same camera again.
I owned a 5D II, then a 5D III, and a 5D IV (as well as a few other EOS bodies).
The III was a huge upgrade from the II in terms of "features" but not so much a huge upgrade (more of an incremental upgrade) in terms of image quality, ISO performance, dynamic range, etc.
The IV is different... it is a huge upgrade all the way around. Whether or not you would use all those capabilities depends on your photographic interests and needs (for many people this would be overkill). But it's a very capable camera.
I have only had mine for about 10 months, and I love it. I moved up from a 5D2 to the 5D4 and the difference is night and day both in terms of features and performance. Should point out that I am primarily a stills shooter and have used the video features about twice. I hear that people who have used the 5D3 prefer that camera's video function to that of the 5D4.