John Clements has a nice long article about the differences between theatrical swordfighting and the real thing, with an eye on lightsaber fighting in particular.
After a colleague suggested I give a critical commentary regarding the martial value of lightsaber fights in Star Wars fan-films I reviewed about a dozen or so different scenes from the more serious efforts. They were nicely done, but for me the same nagging concerns kept appearing. With just a few small considerations I know these lightsaber fights could have been much, much better. That prompted me to write this short essay on the chance that some of my expertise might be of value to the many talented film-makers. As a non-choreographer, non-actor, and non-fight-director, I enjoy the privilege of being able to freely consider any swordfight in entertainment media exclusively from the point of view of “Would that really work”? Of course, as a swordsman/martial-artist, this invariably means being a critical observer and I make no apologies about that. ...
If the purpose of lightsaber fight choreography is simply to convey drama and excitement within the context of a story, then choreographers feel they've done their job well. But, from my point of view, if a lightsaber fight is supposed to convince the viewer that individuals of great skill are really trying to kill one another with laser swords while using supernatural powers that heighten their senses and physical abilities, well, they fail miserably.
As I see it, the problem with so many of the lightsaber fights in Star Wars fan films, and I am purposely being critical here in my scrutiny, is that there is no real sense of urgency and energy between the combatants. There is no broken rhythm or broken tempo and no sudden changes in the line of attack—they looked choreographed. Often it comes off not like a fight, but a dance routine they’ve done many times before. They lack the subtle sense of shifting balance and leverage and the dynamic hesitation that regularly occurs in strenuous swordplay. Instead, you invariably can see the fighters purposely, purposely, trying to hit one another’s weapons. In some cases, there are even minute pauses as one performer waits momentarily for their partner to catch up, or else slightly delays his own move just until the other is safely ready for it. I suspect that if instead of the cool special effects you were to replace them with plastic toy lightsabers, the problems with the scenes would really show up much more clearly.
And there's lots more. In short: the fighters don't look like they're actually trying to kill each other.