Everyone loves to crap on the ANH duel because of it's simplicity. I think it's a loving tribute to the Kurasawa films that inspired George. Fans also rave about that fan edit with all that flashy stuff that tonally looks completely out of place because all the camera work and moves are way too modern in a late 1970's movie. As much as I enjoy the choreography Nick Gillard did for the Prequels, I much prefer the simpler, character driven fights from the OT. The fights didn't have to be flashy to be effective. They were the literal conflict manifested from the emotional conflict the story created. If you create relatable characters with believable stakes, the action is only enhanced.
People who crap on the ANH duel don't know s*** about actual sword fighting. All the flashy cinematic stuff looks super cool and exciting, but would get you killed. The ANH duel is (1) classic jitai geki style dueling, (2) a model of centered footwork and balance (mostly), and (3) designed to preserve maximum flexibility and responsiveness.
Put simply, if you make big, wide swings, it looks cool, but leaves you open to counterattack by an opponent who is fast and balanced. The middle-guard position that both Obi-Wan and Vader take is a balanced, cautious position. Your feet are planted about shoulder-width, your weight is evenly distributed and centered between them, your shoulders are down and your sword is pointed towards your opponent. From this position, you can respond to almost any attack with relatively minimal movement which preserves energy and also allows you to recover to your guard position quickly if you need to. It's a basic stance that you can use to transition to any number of other positions (naturally, since it's in the middle of pretty much everything).
I actually think the AOTC fights between Obi-Wan, Anakin, and Dooku are the worst of the bunch because of how they're edited. They look flashy when you first see them, but if you watch more closely, it's a mess of close cuts with flashing lights around them, facial expressions that are cropped REALLY close to hide that Christopher Lee couldn't actually do his own sword work (which he's admitted nonchalantly) because he just wasn't fit enough for it anymore (I absolutely believe he could've done it in his prime, though), and probably to give the scene "drama." But much like the fight sequences in the Bourne films, it ends up feeling much more chaotic and incomprehensible, which for me totally undermines any drama.
When Dooku severs Anakin's arm, it just feels arbitrary and dumb. Like...why was he able to do that there when he couldn't do it earlier? Why didn't Anakin block the attack? None of it makes sense.
Meanwhile, the Vader and Obi-Wan fight in ANH has them probing each others' defenses, maneuvering around each other to try to find a good position, and mostly being evenly matched because neither can break the other's guard (and Obi-Wan isn't even really trying to, which becomes clear later). It's a great scene. It's just not a modern, flashy, spinny-spinny-choppy-slashy scene with big, sweeping movements that'd get you killed in real life.