Well, a few things.
The Amerinds would wipe 90% of them out, including all the ones of impressive size. It's not a matter of weapons, though it's worth remembering that the first immigrants from Siberia were already big game hunters. Humans have fire, and that is enough. They could drive almost anything away from the choicest watering holes and food sources, and would burn out the thick woods deliberately to give them better hunting grounds. It might even be easier to get dinosaurs to stampede of a cliff than it was for bison. They'd outcompete pretty much everything, and outcompetition kills you just as dead as hunting.
You might have smaller Triceratops instead of Buffalo, but they'd still be nearly annihilated and end up trapped in the bounds of Yellowstone and on specialty farms. I'm not sure how thickly feathered Struthiomimus and Gallimimus types could get, but if they got total cover, they might have a shot at the niches of deer, elk, or moose. I somewhat doubt it, though. There's also a distant shot that you'd have something like a Hypselophodon or small Pachycephalosaur surviving in the Rockies or South America, instead of llamas or taipirs or deer. The last groundsloths died out around the time of Columbus' arrival, so if you are very lucky, you might get a few European witnesses to the last of the medium size Dinosaurs.
Domesticated animals just aren't in the cards here. In fact, if dinos are filling the llama/alpaca niche, there will be even fewer domesticateds. And if there could have been any domesticated dinos, I promise you that they would not be carnivores. And if we handwave it so there are domesticated, carnivorous dinosaurs, you still could not ride them. Apologies.
It would be pretty awesome.
