I've never played rolemaster, but I understand it to be something like this..
One of the useful, but somewhat dull and mechanical features of 3.x is the critical hit system. Criticals deal double damage, or more depending on the weapon. Some feats improve this, and some feats improve how often the crits are done. My players are usually fairly excited to roll a crit, except for my crit-stacking munchkin Epik, but the issues which lead to my asking him to alter his character mid-session are for another time.
When I was in high school, I always did critical hits off the cuff -- if a twenty was rolled, then the die was rolled again, with escalating awesomeness depending on what was rolled from there. A second twenty would result in instant death, but I don't remember this ever happening. Triple or quadruple damage once or twice, however.
Now, as a grumpy thirty-two year old DM, I have been finding myself thinking about a return to older styles of play, including a more fluid system of critical hits, and critical fumbles.
In case anyone reading this is confused as to what I'm talking about, in the game of Dungeons and Dragons, attacking involves rolling a twenty-sided die, trying to roll at or above a target number. In most versions of the game, rolling a twenty would result in a more damaging hit, and rolling a one indicated some sort of failure.
I want to get away from the simple "this weapon does double, this one does triple" of 3.x, and have more solid, consistent results than if I tried to keep it in my head. This means a table. Something simple that operates on a d20, something with results from "oh cool" to "OMFG".
For critical success/critical hits, it seems the second roll for severity should be ascending, so 1 is minimal improvement, and 20 is maximum results. For critical failure/fumbles, it seems logical to have descending severity, but I am thinking that it should also be ascending. I have been thinking about the process of writing up some special abilities/special rules respecting the critical tables, and the rules will be simpler to write if both are ascending. So if you roll a 1, you roll on the critical fumble table, and hope you don't roll a 20. Somehow that seems inelegant to me, but anything that saves an extra 10-15 words I have to squeeze onto a notecard has to be a good thing.
So what kind of results do we want?
I would rather not have an "instant kill" option, but I can't take it completely out of consideration. A high result could cause a foe to be dazed for a round or two, possibly making a coup-de-grace an option.
Something that I'd like to have as a midrange option, in addition to a damage multiplier, would be nervous system shock -- being unable to see or hear for a round makes one an easier target, and lowers one's own attack roll. I don't like having perma-blindness as a possibility, or limb severing. Temporary limb disability would be fair to implement, I think.
I could fill out a table with those three, I think, combined with increasing damage multipliers.
So what about fumbles? Traditional results include weapon dropped, weapon broken, hit teammate, and lost turns. Hitting one's teammate, or "random selection of target within 10'", would probably be at the top of the list. Weapon drop would be at the bottom.
Weapon break is likely to be the most controversial at the gaming table. Players are, unsurprisingly, very attached to their magical equipment. Elendil might have broken Narsil, but that was in a cutscene. Bilbo or Frodo breaking sting on a bad roll would have just seemed unfair. I have a way to get around this, however.
I am planning on ruling that only one component of a magic weapon is enchanted. Everything else is conventional, and required to be of high quality and maintained to keep it in working order. With a sword, the grip could be non-magical, and could be compromised. The wooden stock of a crossbow or rifle, or the bowstave of a longbow would be magical. The magic part won't be broken, but the other components might be. Perhaps a magic sword without it's grip would cut viciously into the wielder's hand. The amount of repair work required to restore function is something that should probably be something that requires ten minutes to an hour of work for a person with appropriate weapon proficiency (as they are able to maintain their weapon)
"Lose a turn" sounds good from a gamist perspective, but should definitely be described creatively, something like the player slapping themselves with the flat of the blade, or stinging their fingers when losing grip on the bowstring. The players should be encouraged, as with much of the critical table, to declare the way in which their character failed. Pratfalls can be memorable, as much as gallant victories.
Dropped weapon would be move-equivalent to recover from, in general, but might not be possible if engaged in melee. Perhaps dropped weapon should be made more interesting, like the weapon is not just dropped, but flung d6*5 feet in some random direction. This kind of mechanic makes a backup weapon important to a well-prepared hero.
I have been considering, along with critical tables, including some luck mechanics -- maybe some special ability specific to thief-types, which allows a greater chance of getting a critical. Or the ability to occasionally add a d6 to the roll for severity of the critical success. I have been noodling over having a relative danger in adding the d6, where another d6 will be put on the table, waiting to be added to the next critical success or failure rolled by anyone.
That's it for now, just throwing out some thoughts.