Hard to say.
In the case of Spain, anti-terrorist laws have shrouded a veil of secrecy about police interventions which adds over francoist habits never adequately purged. Spain has received many complaints of racial bias against minorities in stop-and-frisk operations, and they are accused of using much more violence against [non-Spaniard subjects (link in Spanish])1non-Spaniard subjects(link in Spanish).
EU officials have chastised the Spanish police for lack of adequate treatment of people with mental disorders, migrants in detention centers and excessive use of force by anti-riot police against demostrators.
How does that compare with other countries, though? It's even harder to say. For starters, it does not look as Spain's problem are unique. Germany topples Spain in denounces against the police for violence against minorities; Spain's deaths of detainees while in custody double that of the UK, but are a third of France's (link in Spanish). An EU study focused on Belgium, Bulgaria, Greece and Romania detected the same type of problems with racial bias on their respective police forces.
In general, I'd say that Spanish police is about average for a european country in their use of violence, so is, a tiny fraction of the violence you would routinely experience in the USA, and about thousand times less likely to be killed by them.