Though it was a challenging book to read, I enjoyed the plot of *Huck Finn*. Huck's improper grammer confused me -- though it looked like Shakespeare next to Jim's dialect -- but made his character more believable. Had it been written in proper English, Mark Twain would not have been able to use racial slurs and dialect that was common to the time period.
Tom (the most annoying character ever) provided contrast to Huck. Though he only appeared a few times, I think he provided an important role in showing the emotional changes Huck went through. While Tom was still in his fantasy world (that Huck used to share), Huck saw the seriousness of Jim's situation and wanted to act. I may be going out on a limb, but I think Huck and Tom's relationship is  synonymous with Jim and Huck's. Jim -- who obviously had a rough life -- was the 'realist' in the relationship. Huck wanted to explore rafts, and return to town when it was imprudent to do so. In another instance (when Huck and Jim were discussing languages) Jim showed his simplicity by saying all men speak English.
Huck Finn's adventure was an exciting one, and I hope we read more excellent authors like Mark Twain.