In taking a break from my Subspace-fighting in Brawl, I fired up my half-finished "Hard Mode" file of Shadow of the Colossus. I was reminded of a bit of realism in that game that I wouldn't mind seeing in a future Zelda title... but it could be a good thing or a bad thing or both depending upon perspective...
Shadow of the Colossus is far from a "realistic" game, strictly speaking. Some might say it has more in that way than a lot of videogames, but, really, when your character is able to walk off falls that should break his legs and fights enormous living statues of Things That Should Not Be to ressurect a dead girl who apparently does not rot no matter how long you take, it's not exactly reality. However, the game does add a little realism in regards to the horse in it. Sure, mounting a limping horse in real life is a bad idea and you can't leave them saddled forever or expect them to come to you from wherever when you whistle, but the horse can and does get injured when enemies give you both a good blast of electric antimatter death. The horse will roll and be in distress even as you're flying off it and scrambling, yourself. The horse also steers realistically - as in, I haven't ridden a horse in years, but I remember what it feels like and I was jazzed when I first played this game to find the horse acting like a living creature - namely, the horse fights you sometimes. You want it to turn one way, it wants to go the other and you really have to press that control stick and pay attention to what you are doing to rein it. You can't just run it in a straight line and expect it to go exactly there like you do with ol' automaton Epona.
As said, this can be a good thing or a bad thing. While I was happy to see the horse acting with a bit more AI agency and "more like a real animal" than I'm used to in games, when playing SotC, I have also found myself shouting at the screen "Turn, you stupid horse! This way, dammit!"
Another thing the horse in SotC does that Epona does not: If you shoot Agro with an arrow, the next time you play the game, she will get scared and run away from you whenever you pull out your bow. None of that "You can just go ahead and shoot me in the head, Master," that Epona does.
It's just a little detail... added realism in the mount like I mentioned before. It can be both fun and, at times, aggrivating.