There are some fantastic moments in this serial. The checkers scene where both the Doctor and Jo shush the Master, the moment when the Master panics because he thinks he killed the Doctor for real, Jo getting to be brave and clever in her own right, the overacted fight scenes are fun, and both Benton and Yates are great.

However. The plot has FAR too many aspects so that they all sort of get lost: the dangerous effects of the machine, the hostage situation in the prison, the peace conference being hijacked by a hypnotized Chin Lee (who also doesn't get enough on-screen time post hypnosis), the stolen missile used to threaten a third world war, and Barnham wandering around all innocent because he no longer has his evil impulses. It's just too much, making it almost easy to miss that some of it doesn't make sense: the machine takes out "evil impulses" but then the mind grown from that causes people to see their worst fear and then, somehow, literally die from that fear (not the fear itself but whatever is the cause of the fear, ie actually drowning). At first it seems the evil impulses have just imbued the machine with sentience, but then it turns out that somehow a nearly-impossible-to-kill living creature has grown from them. The Master's entire plan is "start a war that decimates the Earth," which on its own would be amusing and I wouldn't mark down, but with everything together it's one more thing that isn't fleshed out.

The story doesn't even have TIME to get into the problematic and eugenicist issues with choosing to (or even having the ability to) remove evil/criminal impulses from a person, beyond a couple throwaway lines at the beginning.