Yeah dude movement!! art of combat can be really cool with a high mobility system not something like assassins creed which is rly cool but something similiar, the idea of interact with the enviro/props. well im in the same lane with cmcginn :P, but if u want different ideas a talent system could be a MAJOR FEATURE, so you can unlock different sword styles, katana, saber, rapier, etc… (different weapons, different combat styles) & combo system based on those talents 
aaaaaand maybe im annoying but including dodge/ stealth skills could be cool as u know a combat system is not only based on deealing damage some tactical skills can be included u know. thanks for reading 