While posting in this thread it occurred to me that what I value most in an RPG combat system is deadliness. And this is because I want combat to be something players think twice about: I want the decision to engage in combat to be the most important and weighty kind of decision in the game.
This is not because I'm one of those people who is of the view that real combat is nasty and horrible and people should resolve conflicts in make-believe games peacefully. Real combat is nasty and horrible, but fictional combat is both enjoyable and interesting, and to be encouraged.
Rather, it is because of two related reasons:
a) In order to make players genuinely invested in a game, their decisions have to matter. And as a general rule, in order for decisions to matter there have to be meaningful consequences. If the decision to fight a gang of orcs is a simple one because the orcs are easy to defeat and there is almost no chance of death, then what business does that decision have being in a game at all? It makes almost literally no difference whether the characters have that fight or not - so why have it? At best it satisfies the largely masturbatory impulse to show off how powerful your fictional character is in a fictional universe. I'm not sure what on earth the point of that is; your mileage may vary.
b) I like to reward player skill, and easy combat does not reward player skill: it rewards character skill. I like to play Steel Panthers: World at War, and what I always find interesting about that game is the way it rewards intelligent use of command & control, terrain and subterfuge: in a good, well designed wargame like SP:WAW victory is as much, if not more, about where you concentrate your forces, when you time your attack, where and when you commit your reserves, and how you predict your opponent's moves, than it is about Tiger tanks being more powerful than Shermans. Similarly, in an RPG, I'm much more interested in how PCs pick and choose their fights, try to manipulate circumstances to their own advantage, and use the terrain than I am in the fact that a 6th level fighter can easily beat up a goblin.
Which isn't to say that the actual fight itself should not be one which the players have made easy through their own intelligent play. The crucial point is that, when players win a fight, I want it to be because they are good and clever players and not because they have kick-ass characters with super duper magic swords.