Despite my love for the second game, I never bought Road Rash III, largely due to middling reviews. Having now played it, I can see why. It's still a good game, but the differences from Road Rash II are minimal, with slightly more varied locales and more weapons (which you don't really get to experience, since you carry a weapon from race to race and so effectively get stuck with the first one you grab forever). The biggest change is in visuals, with the artists moving away from clean pixel art to more photorealistic sprites.
And it just makes the game look messy. The main character - the one you're looking at half the time - looks washed out and indistinct ... and even more so when you upgrade your bike and find that you no longer have the coloured band on your clothes.
There is one great addition, though. An opponent called Scab Boy.