it does take a lot of skill points, but once you get there, and get used to using it, you can really dominate.
when fighting enemies that will advance slowly as a group, i hold my army and sally forth to cut them down. by the time the army gets near my line, i've generally killed all of their ranged troops, any infantry that doesn't have a shield, a hand full of their shielded infantry, and either killed or unhorsed all their cavalry.
a few techniques: ride full speed at an opponent. he'll drop his shield to attack. that's when you hit him. once you get good at it, you can generally get the head shot. also, ride near some infantry, they'll raise their weapons, lowering their shields, then ride away from them at about walking speed. they run after you with their swords raised menacingly. you can take out groups of 3 or 4 real fast like this.
i generally do really well in melee with a bow and arrow, and i'm not that fast (heavy armor, moderate athletics). you just run backwards and draw the bow. your aim is bad because you're moving, but it doesn't matter because they're right in front of you. when they drop the shield to hit, you let the arrow go. also, if they're busy fighting your infantry, you can pick them off from behind easily.
here's a cheap but effective move in siege: after the archers are cleared, you can stand near the top of the ladder by yourself and headshot enemies, one after another like nothing else. have your soldiers on the ground to shoot any of their archers that come up to the wall. and glance around now and then for their archers.
you've got to work on the headshot. you get good at the sweet spot after a while. and even knights and lords generally go down in one shot this way.
i can kill any of the unarmored horses in one head shot, two body shots. when knights are chasing you, it's really easy to headshot their horses. you can turn a line of riders into runners with no problem.