...they are generally depicted as antagonists...
...the Romulans are characterized as passionate, cunning, and opportunistic.
It has been implied that Romulans use a caste system. The Romulan contempt for Vulcans, their treatment of other sentient species, such as the Remans, and their need for strict conformity, suggests that Romulan society is racist/speciesist.
http://en.wikipedia.org/wiki/Romulan