I think where a great many RPG games fall down is in the combat rules. However we try to dress up roleplay as a socially interactive hobby that's about character development and playing a part, we love to kill things. This is why most rulebooks dedicate an entire chapter to combat, and generally wave their hands when describing how you should play your character or interact with NPCs or other PCs.
I find the balance of combat rules hard. I have stated previously that I am turned off by complex or heavy combat rules - Exalted being the case in point, but any system that requires multiple rolls to resolve 'I hit him with my sword'.
I am also concerned with the disconnect between real time and combat time.
An example - I took part in a Rifts campaign about 11 or 12 years ago (god, that long?) and at one point we spent over 4 hours playing out a combat that took 17 seconds in game time.
WTF?! That's over 14 minutes of play per second of game time!
I think the culprit was the fact that we all could take extra actions (and had powergamed our characters with this end in mind) and we were fighting some 30+ opponents, however, no combat should run that long unless you're playing a strategy game.
So, how should combat time work? D&D uses a base of 6 seconds per combat turn, with actions broken up into attack, movement and minor actions, as well as a presumption that your character is actively avoiding being hit (hustling, they call it). Broken up like that, 6 seconds seems fair.
The World of Darkness rules use 3 second intervals, with characters being able to perform one directed action, move a bit and avoid being hit, as well as occasionally perform a reflexive action. That's a lot for 3 seconds.
Ars Magica 5th Edition also uses 6 seconds as its turn length, which includes movement, one attack and defence, as well as spellcasting.
Ah, now, that could be the differentiator. Fantasy spellcasting, as used in ArM and D&D, requires a good amount of time to wave your hands about, shout in an arcane and no doubt dead language and possibly burn some incense or sacrifice a goat, whereas WoD magic is usually an innate ability that just requires an effort of will. OK, Mage may require hand waving, shouting and the trappings of ritual, but that's the exception.
So, when asking how long a turn should last, I need to determine what actions the could characters conceivably want to perform in that time. Simple actions = short turns. Complex or esoteric actions = longer turns.
Next question - Initiative, how should it work?
Most games use a stat + die roll, with the highest roller going first. Gumshoe uses a different method - whomever decides to act first, goes first, with the subsequent order of action going in the order in which the players arrived at the session. I kind of like this. Yes, it has no baring on the characters you're playing, and the hyper aware ninja may end up going last because the player missed their bus, but we're dealing with an abstract system, not real life.
I've read of house rules where the players sit in order of their initiative modifiers, and just take all combat in that predetermined order. It's simple, and clearly works for some people.
So, do we need that extra step of rolling a dice at the beginning of each combat? What value does it add? Does the system reward you for going first, or does it treat all actions as occurring at the same time?
Is it better to be potentially able to kill each other simultaneously, or better to be able to gank the other guy before her gets to pull his gun and gank you?
Is it better that Greedo shot first, or Han, or both at the same time?
But I need to decide on one for my system.
I could introduce a new stat - Speed - which could also be used to determine running speed and crap like that, but i'm loathe to do so. More stats equal more complexity.
That would leave me with using the Gumshoe idea, which is that the aggressor goes first, and then decide on some other method to determine order.
How's about: Aggressor goes first. The order of combat turns are then determined by the participants current Luck score, with the highest going first and the lowest going last. Participants with the same Luck score are deemed to be acting at the same time.
It is possible to disable or kill an opponent before they can act.
Actually hitting somebody
How do you fairly determine whether or not you've hit somebody, or been hit?
There's usually an attack roll, but what is that roll made against? A generic difficulty modifier - score 1 success/roll 10 or above and you've hit? Roll against a defence score?
The former can be seen as slightly unfair - players like having the chance to avoid being hit - whilst the latter requires another stat.
Another thing I like about combat in Gumshoe is that your character is not only presumed to be trying to avoid getting hit (like hustling in D&D), they are presumed to be diving for cover as well.
Which translates as -1 defence if you state you're stood upright in the middle of a room, not ducking, bobbing or weaving; normal defence if you don't state anything, and +1 defence if you state that you're cowering behind a 6" thick lead wall (and limiting your attack options in the process).
Ideally i'd like a combat resolution system that just works with the minimal number of die rolls. I've already decided to have flat damage, for simplicities sake, and I am now looking for a 'to hit' mechanic that allows for flexibility and simplicity.
I.E. I'd like it to make a difference if players duck behind walls and over turned tables or use enemy minions as human shields, yet intuitive and easy to resolve.