I once read that the longhorn is actually an auroch-and extinct species. As such, are longhorns very different from, say charleroi cattle? I also understand that longhorns are not easy to farm-they are onery and don’t have as much meat as other cattle.
The aurochs was six feet high at the shoulder and went extinct before 1650.
Longhorn cattle descended from European cattle that went feral. Charolais is another type of European cattle. The species is Bos primigenius taurus.
The other extant species of cattle is Bos primigenius indicus, or Zebu. That’s the African/Asian humped cattle, like the Brahma.
Aurochs (Bos primigenius primigenius) was the parent species of both.
Different breeds of cattle tend to have different characteristics, including temperament, just like different breeds of dogs do. So yes, Longhorns tend to be bonier, have less fat, and a wilder temperament than some other breeds. In general, dairy breeds (e.g., Holstein, Guernsey, Jersey) tend to be more docile and bonier than beef breeds (e.g., Angus, Charolais, Hereford).
Those are separate subspecies, not species. And subspecies definitions are always fuzzy at best.
.and kind of narrow at the hip,
And everyone knew you didn’t give no lip
to Aurochs! 
FWIW, Wikipedia notes the last aurochs as dying of natural causes in the Jaktorów Forest, a preserve for them and other rare wildlife (e.g, the wisent) in 1627. When I read about them in the 1960s, there was supposed to have been a small herd in the Caucasus that supervived the Jaktorow herd, but also died off. I mention this only as a remembered factoid to see if anyone can confirm or refute it, as the Caucasus herd is not mentioned in Wikipedia.
Offhand, this sounds like the sort of question that a Google search would have answered.
How did you manage to type this sentence without the obvious, glaring contradiction staring you in the face, even ignoring the typo?
Heh…Big John…my father had that song on a 45 when I was a kid 
Are Longhorns closer to Aurochs genetically than other breeds of cattle?
Visually, yeah. Genetically, probably not; they’re just one among many strains of cattle, all a single species (probably) that included the aurochs.
Closest living variety is Heck cattle, produced starting in the 1920s by the brothers Heinz and Lutz Heck, who directed respectively the Munich and Berlin zoos at the time, and intentionally backcrossed domestic cattle with aurochs-like traits in an effort to recreate the breed from its genes. Debatable how well they succeeded. Supposedly Charolais cattle have a large reservoir of aurochs lineage as well.
All of the modern domestic cattle in the U.S. are of the same species, and can interbreed easily. I used to raise Corriente cattle (disclaimer: I originally wrote the linked Wikipedia article, and those are my cattle in the picture), which are very closely related to Longhorns. The Corriente breed association, in fact, claims that Longhorns are descended from Corrientes, which in turn were brought over to North America by Cortes. The Longhorn people disagree 
Both Longhorns and Corrientes are lean, athletic animals. They don’t really yield less meat (as a percentage of body weight), but they don’t tend to weigh as much, so you get less meat per animal. I certainly wouldn’t say they’re hard to keep. When it comes to breeding, they’re an absolute joy. Unlike all of the Angus ranchers out here, I didn’t have to spend calving season checking on the cows every few hours and rushing out to assist with a calf puller. The Corrientes just drop the calf and keep on grazing (I exaggerate slightly, but not much).
The main difficulty was keeping the stupid things fenced. I remember one night when we got a knock on the door at about 8:30 pm (after dark). This was quite unusual, and I answered the door with caution. A cowboy stood on the porch and said he’d seen a dozen cows on the highway and chased them down my driveway for me. He paused uncomfortably for a moment and said, “What the heck kind of cows are those, anyway? I was chasing 'em down your driveway and the whole bunch of 'em just up and leaped over your fence!” Yep. You want to keep Corrientes fenced, you either have to have a higher than usual fence or just make sure they’re happier on your side than they are on the other.
Many local breeders interbreed Longhorn or Corriente with beef cattle, and have no problems at all doing it. Definitely the same species.
Holstein cows are quite docile. The bulls, on the other hand, are quite mean and unpredictable.
Well, not always fuzzy, bot often. 
I’d also note that it really doesn’t make much sense to talk about different subspecies of domestic animals. “Doesn’t normally interbreed in the wild” is hard to apply to animals that aren’t “in the wild”.
Yah, that. Wasn’t thinking of bulls - don’t all the dairy breeds tend to very difficult bulls? I know the Angus bulls we had were really quite calm and friendly, as much as Angus ever are.
I think the best adjective for most of the bulls I’ve encountered is “unpredictable.”