I second (third) M&B. Couched lance charges are glorious, netting you hundreds of points of damage if you pulled them off correctly (in a game where the player character and most enemies have between 40 and 200 HP, I think). Damage depends on your speed and whether you can line up the shot as close to directly in front of you as possible without your horse actually running into something first. They're probably the most fun part of the game for me.
They also make enemy cavalry really dangerous. You can dodge or parry lance charges, but if they flank you and you don't see them coming, you're toast. I almost always have to target mounted enemies with polearms first.
Spears more generally were a put underpowered, I think, though I may just never have been any good at them. What's interesting in M&B is that relative velocity matters. If you're both standing still with spears, you do minimal damage. During an infantry charge or against a charging enemy, they could be absolutely devastating (though a nice two-hander usually does more damage, thus the OP remark). What's more, the piercing damage effect is great for taking on heavily armoured opponents.
Longer axes and the like are extremely important for keeping enemies at arm's length in a game where you die if you get outflanked on foot. Period.
Enemies react to getting struck. If somebody is preparing for an attack, you can make them lose their footing, stopping the advance and the attack at once. Hit them hard enough and you can knock them over.
What this partly gets at is that weapon variety matters in this game. I prefer to do it all and have a one/two hander, like a bastard sword, and a lance. The lance is for charging enemy cavalry and heavily armoured units, the bastard sword is for hacking your way out if you come across lightly armoured units. On foot, the lance can help resist a charging enemy, and then I switch to the sword for hand to hand combat. One/two handed for the option to use a shield to deal with enemy ranged attacks. Otherwise, just having on your back provides some defense bonus.
Fuck, it's a good combat system.