What makes a battle or combat scene exciting to read, and what makes it drag on or detract from the narrative?
Brevity. My answer to this question is, unfortunately, not going to be littered with nearly as many examples as I would like. I like brevity. Get in, kick some ass, and get out. That's what *helps* to make a fight sequence exciting to read. The longer a fight lasts, the more likely I (and other readers) will lose interest. I don't want to read about every swing of the sword or about every punch. Cover the salient points of the fight, make it feel original even if it is a fairly standard fight, and don't over do it. All I really need to know is what happened in the appropriate number of words.
Of course, after that first statement of brevity I go on, and on, and on a little bit more.
Go take a look.