There are a lot of code metrics that float around, measuring lines of code, code complexity, number of classes/methods, test coverage, etc. The important thing there is to remember that all of those are fairly meaningless.
When measuring the quality of a code base, maintainability is the only thing that I care about in a code base. It breaks down to a lot of smaller values, but in the end, I look at the maintainability score as the sole parameter that I care about.
Tests helps, and intent revealing, well factored code is manna from heaven, but it is important to remember what they are there for. To make the code maintainable.