The Problem With Lightsabers
So... I'd like to talk about lightsabers. First of all - look, they're basically magical sword-like objects wielded by space-mages. They have only one real purpose in the Star Wars canon, and that's to be a marker of otherworld-ness associated with Force-users. They look cool. If you're happy to accept them as just being this cool Star Wars thing, then more power to you. Enjoy them! But don't read the rest of this post because it will probably make you sad or angry at me.
Okay, still here? Let's do this. For the purposes of this post, I'm assuming that lightsabers themselves are actually feasible and follow a consistent set of internal rules as seen in the movies. I'm not going to get into the science of 'can this thing be built at all?' I'm going to assume it can be. I'm also going to stick mostly to the movies instead of the expanded universe and spin-offs and whatnot.
Lightsabers are still one of the most problematic weapons ever invented by Hollywood. It has ISSUES, giant issues, above and beyond it being feasible to build one.
It has no weight
This is actually important. Handling a weapon that has no weight is HARD. Try picking up a tube-shaped object around the size of a lightsaber handle and waving it around - this is what a lightsaber feels like. Try doing the same with a cardboard tube, which is closer to what a sword with a physical blade feels like. What you'll notice - or, at least, what I notice - is that handling a sword-like object is easier to control than handling a lightsaber-like object, because the weight and balance of the physical object conveys more information about where the "blade" is.
Sure, you can argue that the Force makes it possible to handle a lightsaber without it, but the point still stands - it's an unnecessary handicap. Why is it unnecessary? Because if they can make a whole blade out of light or plasma or whatever, they could make a physical blade with just the edge made out of the same.
It sucks against ranged weapons
This should be super obvious, but I'm going to say it anyway. There is no, repeat NO reason to take a melee weapon into a pitched battle in an age where advanced ranged weapons are common. Blasters don't run out of ammunition in any practical way; they're recoil-less, one-shot-kill weapons that appear to be just as effective in close combat as long range combat. The whole 'blocking shots with the lightsaber' schtick only works from the front and because every mook in Star Wars can't aim.
Lightsabers in general don't work against a military commander who knows anything about actual tactics. They can't block artillery shells, for example. They can't block flamethrowers, and flamethrowers are even easier to make than guns. The original trilogy had the good sense to never, ever put someone with a lightsaber into a large massed battle like we see in the prequels, and they still had some pretty silly instances of lightsabers vs. ranged weapons.
The handle is round
You wouldn't think that this is important, but it is - lightsaber handles are round. Sword handles should not ever be round, because it means it's impossible to feel the edge alignment of the blade. (The edge alignment is essential because you need to strike with the edge at 90 degrees to the impact area in order to do damage, instead of bouncing off or hitting with the flat.) Now, you'd wonder why this is an issue, seeing as lightsabers technically don't have edges at all, but here's the thing - lightsaber fighting is based on swordfighting with actual blades where edge alignment matters. If you watch any lightsaber duel, it's obvious that the fighters use lightsabers as if there is an edge to strike with.
So the problem here is two-fold - they fight as if it has an edge, even when it doesn't, and the handle doesn't make sense for a weapon with an edge.
Lightsaber ballet, people. Hollywood swordplay is pretty unrealistic anyway (not always a bad thing), but lightsabers turn it up to eleven and make it ridiculous. The fighters whirl around like spinning tops with glow-sticks attached most of the time.
I call it ballet because that's what it is: people spinning around. Spinning 360 degrees in the middle of a fight is STUPID. You can definitely do a 180 - see Jogo de Pau, the Brazilian stick-fighting school that includes some really interesting stuff for combat against multiple opponents - but that's in the context of striking a person in front of you and then immediately turning to defend/strike a person behind you. Lightsaber fights do complete turns against single opponents. (FYI: do this in an actual swordfight and you will get killed. And laughed at. Not necessarily in that order.)
The prequels are the worst offenders for this. The original trilogy stuck to the whole idea of lightsabers being used for symbolism, in duels between Force-users. It's everything made afterwards that's idiotic.
It's not stealthy
One of the few advantages that a blade has over a gun is that a blade is an excellent stealth weapon. A gun is not. A suppressor can't completely eliminate the sound of a gunshot, no matter what you see in the movies; the real purpose of a suppressor is to reduce hearing damage from repeated firearms use, or to alter the sound so that it doesn't appear to be a gunshot. It also reduces recoil and hot gas emissions, which is obviously better for the shooter. But you cannot and will not ever be able to silently kill someone with a gun. A blade, however, is completely silent, and invisible as long as it has a coating to remove the shine.
In comparison, lightsabers are noisy as hell. Activating one and waving it around generates light and sound that cannot be suppressed, as far as we know. Lightsabers intentionally throw away this advantage.
It's not versatile
A lightsaber can cut through most stuff. (There is a list of lightsaber resistant materials on the Star Wars wiki.) But being unimaginably razor-sharp is not an advantage if you want to use this thing in combat, because it means it's dangerous to the wielder, as many people have said before, AND it means that you're automatically unable to use many useful techniques. Half-swording (grabbing the blade with your hand for extra leverage and point control), is impossible. Outside of the razor-sharpness issue, lots of basic defensive techniques are impossible because lightsabers do not have effective crossguards. (Remember, lightsabers are used in ways that mimic swords with crossguards.) So binding an opponent's non-lightsaber weapon is impossible. Most importantly, in my opinion, maintaining control of an opponent's non-lightsaber weapon is impossible. In both cases, you'll either cut straight through it or, if the material is resistant, get your own hands cut off.
Consider a Jedi with a lightsaber fighting a Sith with a conventionally-shaped sword made out of lightsaber-resistant material. If they're equally skilled, the Sith will win simply because they have many more options for attacking and defending.
That crossguard, seriously
I said 'effective' above for a reason. It's stupid, even for Star Wars, and that's saying something. Crossguards have several uses on a sword; for protection, to prevent the user's hand from sliding up onto the blade, to control and bind the opponent's blade, and in techniques such as the famous Mordhau, or the 'murder-stroke'. I'm assuming that the Force-user in this case is skilled enough not to hurt themselves with it, but it's still not effective at any of these functions.
Protection-wise, the crossguard stops a sliding blade before it cuts your fingers off. But lightsabers do not slide, or at least we never see them slide in the movies. Lightsabers bind in a way that sticks them to other lightsabers, or they bounce off.
Preventing the user's hand from sliding up onto the blade only really applies to blades that meet resistance. Lightsabers do meet resistance against other lightsabers, but this never, ever comes up and, as far as we know, is irrelevant to Force-users. If it were an issue, we'd have seen crossguards a long time before this.
Controlling and binding, again, only applies in the case where a blade slides down and can be caught on the guard. Lightsabers do not slide, ergo this is irrelevant.
The Mordhau requires the user to grab the blade and hit with the quillions, which is obviously a non-starter for a lightsaber. Striking with the quillions might work - emphasis on 'might', because that kind of strike doesn't require quillions on both sides of the blade.
See, the problem with lightsabers is that they are not effective nor practical weapons, and in the original trilogy, it seemed clear that they were restricted to Force-users because they were part of the 'religion', as it were. They were part of the zen mystic of Jedi and Sith, rarely seen and largely only used in duels between Force-users. They were symbolic; as Obi-Wan Kenobi put it, 'an elegant weapon for a more civilized age', which is a pretty clear callback to the romanticized views of knighthood and chivalry from the Middle Ages. Notice that Luke goes from using a blaster in the first movie to using a lightsaber and the Force exclusively in the third, highlighting his development from farmboy to Jedi.
In the original trilogy, the swordplay was done by the legendary Bob Anderson, and it shows. Take a look at Obi-Wan Kenobi vs. Darth Vader in A New Hope. Watch how the fighters feel each other out, testing their crossing, disengaging, striking and parrying in precise, deft movements - exactly what you expect from a pair of sword-masters. Watch Luke vs. Vader in The Empire Strikes Back, and it's far more chaotic - Vader is testing Luke, beating him down to the point where he offers him the power of the Dark Side. Finally, watch Luke vs. Vader in Return of the Jedi, and you'll see Luke more controlled, more experienced, and ultimately the fight is an expression of his emotional state and his final rejection of the Dark Side.
This is why lightsabers are so powerful and compelling. Their usage in the original trilogy was almost entirely wrapped up in the mysticism of the Force and how it served the epic story of the downfall of the Empire, and they were used sparingly. Even beyond that, there was a subtle implication that a Force-user could grow beyond needing one at all. Yoda didn't need one, and the Emperor thought they were toys. None of what I've said above really matters while lightsabers are meant to be something more than mere weapons.
Everything after the original trilogy is where it just falls apart, especially in the prequels, because the whole concept of the 'elegant weapon' goes right out the window. Lightsabers become downright silly because they're shoved into every battle and situation, treated like they should be a practical choice when they are not, and used in ways that are frankly insulting to both sensible swordplay and proper storytelling. All the mysticism, the power of the symbol, is totally lost. I would also like to point out that the lightsaber choreography of the prequels was done by stuntmen, not fencers; people who have an understanding of showmanship and flashy effects above all else. Not swordplay. Not storytelling.
So there you have it. Take all of this as the opinion of a swordfighter and writer for what it's worth. I'm afraid I have no faith that the new movie next year will be anything more than the same as what we saw in the prequels, especially seeing as it's being directed by J.J. Abrams and we all know what he did to the Star Trek movies. Still, I'm prepared to be pleasantly surprised.
I'll write a more complete post at some point about the use of lightsabers in the prequels, and trust me... it will not be pretty.