It is very unusual how long it took the jury to reach a verdict because the case involved a black man. Even more, the case involved an attack by a black man of a white woman. The fact that it took as long as it did shows that Atticus scored a few points and made the jury consider all the evidence.
While the jury does convict Tom, in some ways it can be seen as at least promising that they considered the evidence that Atticus presented during the trial.
The conviction itself is not surprising, because even Atticus knew that he would most likely lose the case. Racial inequality was a theme in this novel, and Tom really never had a chance at a fair trial.