A hammer should be able to cripple a target. Break limbs, smack the enemy. Harder to block, slower to swing.
An axe will have a great deal more percussive power than a sword, due to its greater mass concentrated along a smaller striking area. It will therefore do a much better job of battering plate or destroying a shield. That's axe damage: swords tend to splinter and chop off pieces around the edges, but an axe will go right through in the middle...
Furthermore, the sword is very quick and versatile in both attack and defense. It thrusts better and has a nominally longer range.
Armors should feature weaknesses against each weapon. A sword will obviously wont do much against plate armor. A hammer can thrust it and cause much more impact.
Limb system: Each character should have limbs health, based on each part of the body. I believe it would work well. Hammer users for example could break the bone of someone's leg. While sword users could use quick slashes to damage it and then, finally, cut it off.
Schools of hand-to-hand. Similar to Magic schools. Different techniques, based on something different. It could be, offensive or defensive. Maybe unarming the enemy, submissions, fatal attacks or even elemental attacks.
Please share your thoughs and also share your suggestions.