Literary critic Michael Patrick Hearn describes Williams as "an indifferent draftsman, his pictures varying from coarse to the highly sentimental". Regarding his work in Tom Sawyer, Warren Chappell writes "it is evident that Williams did not always take care in reading the text. As the first man to do the whitewashing scene, he carelessly used a rail fence instead of the board fence which is described." Williams was also known to incorporate subtle humor into his illustrations for Tom Sawyer: he placed his own name on a gravestone in one scene, and in another it has been suggested he deliberately altered the lettering on a sign reading "The pen is mightier than the sword" to appear "the penis mightier than the sword", a pun which Twain himself used many years later.
