adywan, here's a couple of other things to do with the 'gantry duel' sequence that I wanted to mention too, in case they can be tweaked a little -
1. ....at this point below, near the end of the walkway, the railing on the left-side of Vader is intact until it's struck by a lightsaber....
2. ....and when Vader passes that point, we now see that a 'cut' has been left through the railing. Although there are small 'gaps' between the tops of the railing anyway, this one has definately been added after the lightsaber strikes....
( it can be seen more clearly in this bigger version - http://img511.imageshack.us/img511/3606/screenshot147.png )
3. ....and then moments later, the railing on Vader's right-side is struck by a lightsaber too....
4. ....which leaves a 'cut' through that railing as well....
( bigger version of shot above - http://img146.imageshack.us/img146/24/screenshot167.png )
5. ....however, just jumping back a little, when Vader first swings his lightsaber downwards at Luke in the shot below, it seems he strikes a railing first....
6. ....and then strikes against the side of the doorway when he takes another swing at Luke, who ducks....
7. ....thing is, when vaderios previously did a mock-up ages ago showing two 'scorch marks' near the doorway in the 'close-up' shot below, I remember agreeing this would be a neat addition, but that there should perhaps only be a single 'scorch mark' from Vader's swing in shot 6.
However, if you agree that Vader does strike the railing first, then when we cut to the 'close-up' below, it would be good to see some kind of 'cut'/'singe' damage indicating that too, similar to the damage seen on the railings moments later in shots 2 and 4....
The current 'gap' seen in the 'close-up' railing here is part of the actual railing design, but perhaps it can be made slightly bigger, and 'sheared-off'/'singed' somewhat?
....and perhaps the same thing could also be done to this shot below which comes a little later (just before Luke hits Vader's shoulder armor), where Vader has just swiped down at a point where there is also already a narrow 'gap' in the railing, yet it remains exactly the same thin width after the sparks have gone....
This next point which involves Luke's tunic always seems really jarring to me, but it's something else you may just be able to improve a little -
....although the slight raggedness on Luke's tunic seems to be different during certain shots, both shoulder seams are generally intact in the run-up to getting his hand cut off....
....but when we cut to the shot below, the tunic he's wearing here has suddenly developed a severe rip on his left shoulder....
....yet when we cut back to various shots of Luke afterwards, his left tunic shoulder is now suddenly intact and sewn up again....
If Luke's bare shoulder 'skin' could be made to match the colouration of the tunic somehow during that particular shot, then things would be less jarring I reckon. See what you think anyway.