I think a good battle scene is one that keeps the action going, and is just descriptive enough to give a general idea of what is happening, but does not get so bogged down in verbiage and description as to stall the whole thing. Battle/fight scenes need to feel fast paced and immediate, though of course there can be mini scenes within those larger ones that slow the action down, and give the reader a better view/insight into what characters are doing and seeing. An example of this is the Harkonen attack on the Atrteides in the first Dune novel. That scene is masterful in the tension it creates through the grand sweeping action, as well as the little things is focuses upon, like the two or three sentences devoted to what a laz-gun does when it is set to explode. The attack on Helm's Deep in The Two Towers is another example of this, to a lesser extent, though Tolkein does allow the action to wane at times. Still, I think these are good places to look.
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