An old money equestrian sports themed world wouldn't have opened my wallet, but I'm the player who is still waiting for a proper slum, so there's that.
Chestnut Ridge is pretty much the only world matching the browns of Batuu, so I'm stuck with it and have taken quite the liking the that world, but I prefer to play my horses in Moonwood Mill (many of my sims own descendants of the old sawmill workhorses) and Henford.
My gripes are minor; there could be more fun items than that ball, genetics are boring, throwing occurs way too often and I miss an option to stable horses externally. As of now they will forget their owners if moved into a different household and a sim riding a horse that isn't part of their household can not enter competitions.
I also dislike that saddles are cosmetic only, compared to Sims 3, where a horse wearing a saddle for too long grew uncomfortable.
Lastly, with many simmers running involved medieval saves I'm surprised that there aren't knights themed saddles and costumes as CAS options.
Long story short, I don't feel fatigue setting in yet, to the contrary I plan another playthrough of the Oregon Trail challenge sometime. It would be my first one with real horses. (The challenge moves the sims to a different environment every week, it's not restricted to western-themed worlds.)
I think it really helps that I'm neither an expert on horses nor particularly interested in how breeding and competitions really work. For a layman, they just add atmosphere and new things to do.