The end of every legislative session brings on the desire to "rate" a legislature. From media outlets to advocacy organizations, the end of session report card or evaluation tool for a legislature is largely based on the ability of a legislature to deliver on the priorities of the organization producing the report card than on the actual performance of the legislature.
Perhaps, it would be better to characterize the end-of-session rating as a reflection on the ability of the media or organization to influence the outcome of a session instead of a reflection on the legislature itself. This, however, is much less satisfying to the clients who receive reports of work from exhausted lobbyists or editorial boards who would prefer to opine judge legislators on their ability to produce results without the responsibility to actually advocate for them.
Thus, measuring or grading legislative performance is a truly difficult task. As a starting tool, one should look to what the Oregon Constitution requires of legislatures. They must meet annually and approve a balanced budget. Very little else is required of the legislature in the Constitution. In fact, much of Article IV that governs the legislature is about what the legislature cannot do instead of what they should do. Our founding fathers (and mothers) knew that legislatures would find a way to legislate as much as they could, so better not to direct them, just limit them.