I am not entirely sure how I feel about this story, even after a third play-through. On the one hand I appreciated the setting but I found the piece as a whole to be a little confused with baffling character motivations and a lack of focus at points.
I felt Leslie Phillips was okay as Knox but I found his performance to be a little flat at times. It is possible though that I found the character a little tough to get a handle on because I had not heard his first story, Medicinal Practices. I cannot say though that this appearance has made me keen to seek it out.
In contrast though I loved both Colin Baker and Maggie Stables here. The latter is particularly suited to these sorts of historical yarns (her character being a history lecturer), while the sixth Doctor seems entirely at home in a theatrical setting like Ford's Theater. The good chemistry between the pair is very evident here and Ross has a good handle on their style of banter.
As for the story itself - I liked the concept of the tale and enjoyed its first two parts but struggled with the second half. The setting is interesting and the idea that Booth might be killed before assassinating Lincoln is explored well but I tuned out when the monsters showed up.