ubernovatsunami: Maybe its just me then.. but it really does seem like every damn bump, branch, bush and bird causes my horse to freak right out and hit the brakes like we've hit a cliff or something. Even rough surfaces like old bridges cause this, ack.
You're fine, horse is fucked.
Roach's behaviour looks like either improperly built or improperly tested. For example, as you sad, she is great bump collector, going from full speed to all "neigh" on plain surface with no obstacles around. In same time, it can rush towards obvious obstacle (a wall, high enough, so she wouldn't be able to jump over) and run into wall, not stopping. given control input lag, she can keep running even after you release "shift" key. Sometimes she can run into people without slowing down, in another time she will stop when there is anyone ahead.
In same time, she can jump over certain obstacles automatically (I haven't pressed spacebar), like small creeks or slopes. I don't really know what is bug and what is feature here, but according to my family, during playing Witcher 3 I already cursed more, than during previous months this year, even while playing GTA V, which was far from puhfect, but at least in most cases was predictable.
Besides, when Roach is galloping on the road and you don't touch directional controls (forward, left, right), her stamina is not decreasing. But as soon you touch these controls, she starts losing stamina. WTF?
ubernovatsunami: Anything good and exclusive from the horse races or may I just skip it?
You can skip it, as I got best equipment as loot or bought from traders. IIRC Zerrikanian saddle (+80 stamina, best so far) was found as loot while rugged saddlebags (+70 carrying capacity) and zerrikanian blinds were bought. So racing is kinda pointless.
Oh, some minor spoilers - if you still want to participate races, exercise manual steering as Roach tends to collect everything on the way, and in Novigrad races beware of third run (by the way, unlike Velen's, Novigrad tracks are different) - track does 8 figure there, and I got my waypoints wrong (one of glitches that started flooding game after entering Novigrad), game sent me back to the part I already visited. Thankfully Roach decided to stop and my opponent got forward, showing me way. :)