One of the unique things about Larry Niven is the way he deals with aliens. Of course different writers come up with different ideas of what non-human sentient species would be like, but Larry Niven's ideas are rather interesting.
This is primarily because he bothers to set up an elaborate social structure for each of the species he introduces. For example the Moties (Mote in the God's eye) have a social structure where everyone fits into a particular occupational niche. The Pak (Protector) (who incidentally are the species from whom humans descended) have a different culture with emphasis only on reproduction and survival. Puppeteers are cowards, Kzin are insanely aggressive, and the Outsiders are probably the most interesting(and romantic) of all. They spend their time making trips to the galactic center and back at sub-light speeds tracking starseeds.