This is a compelling fantasy. So much so that other writers have trodden the same ground, most famously L. Sprague de Camp in "A Gun for Dinosaur".
Bradbury makes the tale slightly different, by bringing in one of those time paradoxes that the true science fiction fan will happily spend hours debating. Bradbury's twist is that one of the time-travellers steps on a butterfly and screws up the subsequent course of evolution.
Now many have criticised the story for its logical flaws - most famously the editors of Fantasy and Science Fiction who rejected the story on those grounds. (Bradbury didn't care - he sold the story to a 'slick' magazine instead, and made a whole lot more money.) However, defenders of the story, myself included, will tell you that the details of the time travel don't matter one jot. It's the symbolism that's important. Bradbury seems to be saying that little things are important: the way he sets the story up, the fate of the dinosaur is trivial; it's the butterfly that really matters.
Looking at various visual interpretations of "A Sound of Thunder", I find that most illustrators have gone for the big picture. They show the T.Rex, sometimes dwarfing our time-travellers. That's certainly true of Frederick Siebel, the original illustrator of the Collier's magazine version of the story (June 1952, above). Notice that Siebel gives us the thrill of the hunt. He does also show the all-important pathway which our heroes must stick to - and one of the hunters fatally stepping off the path.
Franz Altschuler, who illustrated the story for Playboy (June 1956, above) follows the same idea, although the chrononauts don't seem quite so concerned in his vision.
Even the Game Boy game (above) bearing the title of Bradbury's story lingers on the hunt.
The poster and publicity for the recent film version (not a film I recommend you rush out and see) did get one thing right: emphasising the butterfly. I think this adds to the intrigue of the advertising campaign, especially when the movie trailer hints at sub-Jurassic Park dinosaur CGI. (Image shows the movie poster graphic used on a re-issue of a Bradbury short story collection.)
[For the record, I find the low budget adaptation for TV's Ray Bradbury Theatre to be vastly superior to the Peter Hyams movie. And the radio production for Bradbury 13 is pretty good as well.]
Full marks go to Joe Mugnaini, the quintessential Bradbury illustrator, for achieving such a perfect balance in his line-drawing. Created for The Golden Apples of the Sun, the short story collection that first contained "A Sound of Thunder", his illustration (above) seems to focus on the dino hunt - and his composition uses the pathway as a flourish that frames the tyrannosaur. But look again. See how the butterfly, all translucent wing, dominates the scene.
This, for me, is precisely why Mugnaini worked as Bradbury's best illustrator. He found a way of getting narrative into a single frame, and always gives a new way of looking at a story.