1 Monty: Excalibur is just a legend, Dad. King Arthur is just a legend! Even if the man existed, he didn't have a magical sword.
2 Prof. Jones: I beg to differ. I've attended meetings in the past with all the other top Arthurian scholars in the world.
3 Prof. Jones: We held a round table discussion and talked long into the night, every night.
4 Prof. Jones: So you could say—
4 Monty: If I agree to go will you never, ever finish that sentence?
4 Minnesota Jones: Where are we going?

Yea wikily*, Excalibur is described as a "magic sword" and as being "attributed with magical powers", but it's not actually clear what magical powers, if indeed any, the sword is supposed to have. There are some vague assertions that the sword shone brightly, and blinded some of Arthur's opponents in battle, and that it possessed sharpness and strength beyond that of normal weapons. But these are not exactly your flaming dragon-slayer type sword with three wishes and the ability to detect treasure and drain life energy levels from your opponents type powers.

Interestingly, Excalibur's scabbard actually seems to be credited with significantly more genuinely magical ability. Depending on the exact version of the stories, the wearer of the scabbard could not die from battle injury, or would not even bleed from wounds at all. That seems just a little more useful than having your sword be shiny and a bit sharper.

* i.e. According to Wikipedia.