Re: whirlwind, I was having a similar discussion with a friend, and I brought up the point that I had recently done warrider damage three times in rapid succession on alternating sides of the horse, and that's enough of a special attack for me.
Since you're basically in total control of the attacks, the question is-- what special attacks can you pull off? It kind of makes it an interesting added challenge to the game.
But I like the point about "stunning."
Too often I've been charging by at full speed on a courser, swung a war sword at some dude, and he blocks with a wooden club, which fully absorbs the blow. Wtf? No! I'm not expecting damage, but he should be scrambling to his feet by the time I'm circling for the second pass. An easy way of determining this is perhaps that blocking warrider damage knocks you over, but only in a world where it's easy to get back on your horse. ("Call horse" shortcut?)