I read through all the answers, and I noticed nobody mentioned code complexity.

There's a tight correlation to code complexity and readability/maintainability. There are numerous code complexity scoring algorithms, but I'll just talk about how McCabe complexity scoring works.

Basically, McCabe scoring reads through your code and computes the number of unique "paths" there are through it. If you use McCabe as your numerator and lines of code as your denominator, you get a pretty good approximation of "readability" as well.

If you've got 10 lines of code, and there are 300 paths through that code, that is some pretty unmaintainable code (difficult to change safely and easily), and it's probably not very readable. Conversely, if you've got 300 lines of code, but there is only 1 path through it (it has no conditions), it's both readable and easily maintainable.

Where McCabe falls down however is in that latter example. If I've got 300 lines of code with no conditions, there's a really good chance I've done "copy/paste reuse", and obviously that's not a good thing either. So there are system-wide metrics that you apply in addition to McCabe -- like duplicate or near-duplicate code detection.

I read through all the answers, and I noticed nobody mentioned code complexity.

There's a tight correlation between code complexity and readability/maintainability. There are numerous code complexity scoring algorithms, but I'll just talk about how McCabe complexity scoring works.

Basically, McCabe scoring reads through your code and computes the number of unique "paths" there are through it. If you use McCabe as your numerator and lines of code as your denominator, you get a pretty good approximation of "readability" as well.

If you've got 10 lines of code, and there are 300 paths through that code, that is some pretty unmaintainable code (difficult to change safely and easily), and it's probably not very readable. Conversely, if you've got 300 lines of code, but there is only 1 path through it (it has no conditions), it's both readable and easily maintainable.

Where McCabe falls down however is in that latter example. If I've got 300 lines of code with no conditions, there's a really good chance I've done "copy/paste reuse", and obviously that's not a good thing either. So there are system-wide metrics that you apply in addition to McCabe -- like duplicate or near-duplicate code detection.