Man, it must have been a bitch getting the motion capture rig on that horse.
Here's a fun way to pass your time: get off the horse and just watch the main character and the horse idle and fidget. It looks more lifelike than just about any other game I can think of; most 3rd person games have the main character run through a single, predictable, robotic loop, maybe with an occasional fidget thrown in as a flourish. Not Shadow.
So, power of focus: boss-killing, and horseback-riding. Both done extremely well. But it does kind of get boring after a while; you kill a few bosses and then you go do something else, and that's where the multi-games like GTA get their power. The horseback riding is enough to give you some variety and vary the intensity, though.
And not to beat a dead horse here, but the most underrated game of 2004, Galleon, did the climb-up-on-the-boss and kill him thing first. Not as well, granted, but that's focus for you.
<em>Shadow</em> must have the worst framerate I've seen in a PS2 game. I'm surprised the reviewers didn't ding it more for that.
Still, all in all, add it to the list of heartbreaking games.