A particular problem is that the reviews don't have much hindsight, because they're mostly filed by students currently in a course, or those who just completed one.
I believe I could now say with reasonable confidence who my better undergraduate professors were, and who the worse ones were. But if you had asked me to rate each professor during or immediately after the course, I would have made different choices, which in retrospect were probably not the right ones. It's very hard to evaluate introductory courses, in particular, until you get a few more courses in, and realize that some laid a good foundation while others didn't.
I believe I could now say with reasonable confidence who my better undergraduate professors were, and who the worse ones were. But if you had asked me to rate each professor during or immediately after the course, I would have made different choices, which in retrospect were probably not the right ones. It's very hard to evaluate introductory courses, in particular, until you get a few more courses in, and realize that some laid a good foundation while others didn't.