The Godot documentation is good not only because it gives explanations and examples, but it also serves as a learning resouce
If you're bored, it can be pretty fun to go to the Godot documentation and learn something about Godot or game/engine development in general.
Godot also does a good job making sure ALL documentation pages are eventually updated to be accurate for the latest version
The Unreal engine C++ documentation is bad. Some of the pages don't even have words describing the types. Only links to different functions.
The excuse given for this is that you can read the engine's source code that is well commented.
But that raises the question on why the documentation even exists then.
Source: a 40 minute long video
The Unity engine has documentation for almost all of the engine features, but there isn't a lot of variety in the examples (there is usually only one or two examples that do not cover all use cases of a feature)
Another problem is that almost every page of the documentation has different Unity versions. This means that there is a ton of variation on exactly how out of date each page of the documentation is.