...well, they decided to replace races, how you get build up stats, and subclass levels.
mostly you can slot in 5e options directly, but differing subclass levels and feature interaction make porting subclasses feel very iffy if you don't have a strong grasp on editing mechanical rules safely. mostly, there isn't a simple nice set of instructions you can follow for using 5e options with a ToV based. you have to do a bit of leg work.
Binder