A few things come to mind when I think of requirements that make me happy:
1) I can tell the person writing them knows just enough basics about how data works, generally speaking, to phrase things in a way that satisfies both the mind of the general population as well as supplies me with what I know to begin designing - to both our understanding
2) the requirements do not depend overly on using lingo that is not known to the technical side, or could be open to interpretation, but instead references the Business Systems which are involved - again, in a way that anyone can understand who understands the basic Business Systems. The lingo used should be lingo that has a written definition itself
3) the requirements should not be contradictory in nature
4) whatever internal lingo is used, the level that is used should remain consistent throughout multiple documents, projects, and over the course of time for many reasons but among them so as to create documentation that remains synched and accurate
5) the requirements should clearly state if at some point, the writer isn't sure of something that requires discussion - in other words, they should know just enough to have a sense of when their knowledge may be incomplete enough to write it perfectly and stimulate discussion questions
6) a PM might want this, although I don't care as much: the requirements should demonstrate how they are linked to and support the business process goals/rules
7) the requirements should be written in just a sensitive way that uses great exactness with regard to the desired outcome, but stops short of touching how it should be designed, beyond the outcome desired....this one is a bit fluid, most dev jobs have allowed me considerable latitude MOSTLY in the area of FE design, which frankly, I enjoyed.
the requirements leave me with no questions in a perfect world
Edit trying to answer your question humbled me Jon, I realized that frankly I struggled to do so.
Reminds me of something a supreme court justice said (which is roundly mocked, but makes a lot of sense to most people) once many years ago about public obscenity: something like ... I can't define it, but I know it when I see it!
Which used to be true of course, when the majority of the general population was on a similar moral wave length.
In all fairness to me, however, I suspect the problem isn't that "good" requirements cannot be "defined" ... I suspect that
1) It is extremely context-sensitive; i.e., I can only define what Good means in the context of a particular role at a particular company
2) I'm just not smart enough to articulate it, but the definition could exist