Sword Swing in Progress

Well, alright. I'm not going to say anything about the rig as it's the one pretty much all learning animators seem to use for their attempts. (Which is quite valid.)

The animation looks like a lot of rather aimless swinging and the lower body is completely static. Since we don't see an opponent it should be readable from the character's animation alone where the focus of his swings lie - which at least to me it isn't.
Give the animation of the upper body focus and the actions variety. Instead of just swinging from left to right, build in a forward thrust every now and then, vary the attack angle, make the character pause in his attacks to maybe dogde with his whole body.

Of course, the feet shouldn't just be planted on the ground. Sword fights are very dynamic, part of which comes from the concentrated observation of the opponent's moves to be able to counter them as early as possible. You should look up Olympic fencing on youtube to get an idea of those dynamics.
Opponents don't just advance upon each other, thrashing wildly, they draw near cautiously and circle each other, trying to estimate what the next move will be or trying to find an opening into which to strike. Very often an attack will be met with a counter movement that forces the attacker to cancel in mid-strike, and sometimes attacks are just feints opening the opponent's defence so they become vulnerable at another point.

Of course, from an animation standpoint there's a difference whether you're fencing with a rapier or a sword as swords are heavier. If the weapon is heavy the effort in wielding it should read as well. Think the entire process through very carefully, trying to think like both fighters, what they do, how they react and how each others' actions will influence the other's reactions.