Combat sometimes gets a bit repetitive in any game. Swing-hit. Swing-miss. Swing-hit. Sometimes, the players just get into the habit of saying 'I attack!' and the DM's left with trying to make it interesting. Sword and Fist makes an admirable attempt to give players incentive to be a little more creative. New prestige classes are introduced, as well as new feats and weapons. A good example each of mounted combat and a duel outline how things can be.
So why just three stars? Well, it occurs to be that this book was just a little quick out of Wizards' playtesting rooms. The descriptions for some of the feats are distinctly lacking (anyone care to tell me how to apply the Dirty Fighting feat?). Some of the prestige classes are a bit high-powered (the Ninja of the Crescent Moon jumps to mind). The price is also a bit of a disappointment. Almost the same price as the Player's Handbook, but a fraction of the content, and it's softcover to boot.
In summary, a good buy if the DM's willing to spend a bit of time editing for the sake of sanity, and also if combat's getting a bit dry. If you're doing okay in that department, I'd be inclined to give it a miss.