Over all, it's an interesting take, that was pretty well done.
My "plot" complaints are only that Vader was more animated and mobile than I prefer. I prefer a more pulled in fighting style for Vader, with strong, confident movements. This had more flurishing and reach than I like. And the overlaying of the dialog from the mustufar fight wouldn't be appropriate to have in episode IV.
I enjoyed the concept of obi-wan still being an able, quick, and mobile fighter, though some of his more extravagant movements could be cut down.
My "technical" complaints are just that it's clearly a bit janky. The cgi mixed with original footage stands out surprisingly hard, and the different voice samples used seemed inconsistent sounding and fairly unnatural in the flow of the fight as presented.
That said, it was a lot of fun to watch. I especially enjoyed the reflection of the sabers in Vader's eye lenses.