And Tracy's appearance reflects his...uprightness, I guess. He's mostly made of right angles. They ALL reflect their inner selves. But of course, there's the fact their appearance is often a plot point to consider...
The grotesqueness, and the frank violence--all in a cartoony way!--are what made me love Tracy as a kid. I also like his weird constantly-shifting letter size. It adds serious dynamism to the strip. It's comics expressionism, like Fritz Lang crime films on paper.