Spain has its own load of problems, like any other place. Big cities have lowered their quality of life a lot since the 2008 crisis.
Science is massively underfunded respect to what US was enjoying. Expect cuts in your salary. Physicians earn much, much, less, but students can follow public university studies without being put a crushing debt load around their necks.
Science is also being invaded lately with political and bureaucratic BS. Universities have less resources and are always scammed in the ranks that benefit Asian and US universities.
We expect one month of Holidays each year, by law, or to be compensated for it if we agree to spend this time working. Most researchers volunteer to work extra hours or weekends if needed to finish the experiments.
About cultural differences. There are not "white" people and "hispanic" people in Spain. Is either the same thing, or it does not really matter.
"Negro" means "black", and is just a color. Some people are racist, specially out of the big cities, and even more are classist, but if you are black and people describe you as a man negro or a woman negra they don't mean to insult you, they are just describing you. There is not such ridiculous term as an "Afro-spanish", if you have born in Spain or earned the nationality, you are as much 100% Spanish, as any other.
In fact, you are either Spanish, or foreign. If you learn the language well you "are honorary Spanish". If not, you will be always be the "Moroccan" or the "Gringo", but not the "black" or the "white". Europeans had mixed their bloods for ages and people here consider themselves as much "white" than you (if not more) and will find the distinction offensive by unnecessary.
As long as you act as a reasonably civilized person, only the extreme right idiots will care about your tan. Avoid this European MAGA like the dangerous plague that they are.
In restaurants, you need to call the waiter and say what you want. If you want the bill, you need to ask politely for the bill. Don't wait to be noticed or you will wait forever. You will not be chased off the table normally, that would be rude.
You will receive the amount of food expected traditionally in the area (not the humongous portions normal in US unless you visit the North).
Tips are fully voluntary. Unless you go to a very exclusive place you should tip between 0 and 2 dollars and don't need to argue why. (Forget about that X% of the service. We hate going out and being forced to do math).
People will benefit also of the environmental regulation. I assume that a big chunk of the morbid obesity epidemics in US came from unregulated contamination.
To end, a couple warnings, specific from the country:
In small populations near mountains and forests, wildfire crime is a recurrent problem. If there are cows or sheep roaming wild in the area, expect wildfire mafias. Assure to remove any flammable materials near your house and to have an escape route plan.
Dry riverbeds are dangerous. Engrave this in your brain. Locals use this places as parkings, but will run to remove the cars if there is rain expected. You shouldn't park in this areas, never, ever, try to cross a current of water or rescue your parked car if there is water, and should avoid buying any property in this areas. The place is called Rioseco for a motive. Each year a few expatriates die in the Mediterranean caught by flash floods.