Weapons, armor and tactics are always in a state of balance with each other. As metal working skills improve better swords and weapons are made and the other side of the coin of this is that better armor is also made. Keep this in mind. Better blacksmithing and forging skills is not just about weapons, it is also about armor and fortifications. Offense and defense benefit equally and there is always a balance. This is a medieval arms race that is always moving forward yet always in balance.
One of the biggest pitfalls http://topfirearmssupplies.com/ that fantasy writers can fall into is to make super weapons that have incredible powers. Often times these powers are bequeathed on the weapon through magic. It is too easy to have an ancient sword that was forged by a magical Dwarven blacksmith who captured a dragon and used its fire to harden the magical sword like no other sword has ever been hardened. While this can be fun to write and maybe fun to read you should do your best to avoid situations like this. It is too easy to rely on things like this as ways to get you out of difficult situations.
Remember, everything has to be in balance, and everything has to make sense. If you do have a weapon, say that your hero is wielding, and it has unusual powers, you should balance this with something. What is the cost of this weapon or sword? Does wielding it bring danger to the wielder? Is there a fatigue factor? Consider this. It also adds dimension and excitement to the story. If our hero is hesitant to use the sword it will add a dimension of drama to the story. He better have a really good reason to use it.