Honestly, I'm not sure. I never really got into BR, so I don't know all the nuances (which is the vast majority of the differences). Still, I know some and will list the BR version first.
Armor as Defense bonus (AC) vs Armor as Toughness Save bonus.
Class Toughness Bonus vs no automatic Toughness bonuses.
Minor differences in skill lists.
Built in Setting vs Generic (setting-free) rules.
Corruption rules for mages and those with magic gear vs no such option.
Probably other stuff. Overall, though, they are very close.
Good luck.