I agree with everything swisstone said above, and would add The Seeds of Doom and Terror of the Zygons to the list of good'uns. Most of them are at least enjoyable, if not great; The Android Invasion is the notable exception. And it's still far from being the worst story ever...

Just ignore the rat! (And everything else ratlike in its BBCtastic-unspecial-effectness.) But you coped with the giant robot, so you should be okay (not that the robot is the worst -- far from it -- but it's bad enough).