I think games like the Jedi Knight series and Rune are an excellent example to follow when considering combat. For proof of that their systems really do work, check out the cult following they've obtained while still having 0 advertising or exposure. Couple this with what you see in the original Gothic game, and I think you could have a hit!

Let's look at it this way from a bottom-up design perspective:

You target an enemy by clicking on them. From this, pressing on the WASD you can sidestep around the target in a 360 angle or move forward and backward. Clicking causes you to swipe your weapon - and depending on if you are currently moving in any direction you will swipe differently. Let me elaborate more on this.

If you are currently sidestepping while you click, you will slash side to side. If you are move forward, you will thrust and do overhead attacks. If you are walking backwards, you will do lower attacks on the legs and torso. If you are standing still, you will do a possible combination of any of these attacks. If you swipe while walking forwards(pressing W), and subsequently follow up with an A, then an S, and a D, you will do a round-house type move.

By right-clicking, you parry - and if you parry at a certain timing you will temporarily 'disarm' or throw off the enemy's guard(think Soul Calibur's 'guard impact').

You can hold down shift and then press left-click, and you will kick your opponent. If you hold down right click, and then press shift you will attempt to grab your opponent. If you are successful in grabbing them, you will throw them to the ground. When the opponent is on the ground, you can attempt to perform a "finishing move"(decapitate with an axe, stab them in the chest with your sword, whatever). Of course, if they are not heavily wounded they will get up before you can perform this finishing move.

Interesting? Maybe?

Zephyr, God of the West Wind.