I used to play in a game set in Middle-Earth using the ICE fantasy rules (not the water-down MERPS version). All rolls are percentile, and if you roll a 1-5 you roll again and subtract. If you roll a 96-100 you roll again and add, and this can keep going on and on. Oh yeah, and the system has extensive crit tables that cover varying degrees of success or failure - so a really high roll will get you a really good crit (and vice versa).
Anyway, our DM had a strange knack for rolling the extreme ranges with percentile dice - any percentile dice. Which meant that, every combat, we either got decimated by our amazingly accurate opponents, or our opponents killed themselves without touching us. Like one time an orc managed to slice off the top of his own skull, which then went frisbeeing off into the distance.
One incident which sticks in my mind is when the party entered a room where, unbeknownst to us, several bad guys had laid an ambush. We enter the room, they attack - archer #1 lets go of the wrong end of his bow, gets smacked in the face, falls off his perch. archer #2 breaks his bowstring (we actually had to kill this one ourselves). one swordsman loses his grip on his weapon, sending it point-first into an ally. another stumbles and falls on his sword. yet another swordsman hits himself in the face with his blade, killing himself. Our characters just stood there, watching these guys come out of hiding screaming warcries, only to kill themselves and each other off in an amazing display of ineptitude.
Good times.