The tweaks to the story are surprisingly well thought out. Chen Zhen is actually studying in Japan and in love with a japanese girl. This might be one of the few cases where 90s political correctness actually improved a movie. You can see that they made an effort to be more nuanced and not have a scene by scene copy of the original. Not all japanese are bad guys and the villain, while still being over the top, is actually menacing.
(notice the lack of swirlable moustache)
The real upgrade is the fighting. While Let Li is known for wire-fu (think Once upon a time in China), most of the fight cheoreography in fist of legends is much more down to earth. The speed is pretty high and the stunt men actually know what they do. There is still a lot of tough guy posing, but Jet Li doesn't go as overboard as in the original. There is still a lot of one-vs-many fights with people flying through rooms after a simple hit, but the real highlights are the long and brutal one on one fights. The cinematography isn't as good as some Jackie Chan films, but the editing and the very controlled use of slow motion is top notch.