How long should a fight in a pen and paper RPG last? Different people will have different answers, of course, but there are some consequences of various choices that we can work out empirically. Most RPGs are organized into rounds where combatants take turns and on each turn they can move and/or attack. There are exceptions, of course, like Vampire where it is quite feasible to take 5+ distinct actions in a turn but that system is so totally unbalanced in terms of combat I am going to ignore it for the moment. For HBT I elected to set standard fight duration at 5 rounds. That isn't a battle to the death though, but rather a normal fight where the characters are in some danger but generally win fairly cleanly. A true challenge where either side could win would last significantly longer, probably closer to 8 rounds and a trivial encounter would be over in 2-3 rounds.
DnD Next is currently set at about 2 rounds as standard fight duration. In many cases this means that fights are over on round 1 if all the hit rolls are successful which to me seems totally bonkers. Each player only getting one action? Many fights against monsters that are supposed to be a reasonable challenge ending with the monster not even getting to take a turn? Juh? The balance isn't far off because monsters do plenty of damage in general but aside from monsters that have AOE crowd control like the dragon's aura of fear nothing seems likely to be alive after round 2 unless the party gets significantly unlucky with their rolls. Pathfinder had the same problem I found, in that monsters could easily kill a character from full with a single full attack but those same monsters only lived 1-2 rounds so they rarely got the chance.
I am just not that big a fan of 2 round fights, and even less so 1 round fights. It means that abilities that debuff monsters or buff the group are almost certainly useless and that setting up moves is almost a laughable proposition. The only thing that matters is piling on more damage to end the fight even faster. It also means that combat is massively swingy and random because the monsters can kill the party in 3-4 rounds so it only takes a couple rolls to go the wrong way and the party is going to be wiped out. The more random the fights are the easier the encounters have to be to make sure the party doesn't just die to a fight that wasn't supposed to be a challenge.
I am sure there are people out there who want combat to be a single attack roll "I chop off his head!" but I suspect they are very much in the minority. I think most people want a little more than that and unless the damage to HP ratios in DnD Next are dramatically changed fights are mostly going to be a swing or two in duration.