It's ironic and at the same time turns all of Rainsford's past ways of thinking around on him. There isn't much difference between Rainsford and Zaroff. They both are compassionless hunters who see themselves as classy individuals. The difference is where each one draws the line as to where hunting ends and murder begins. For Zaroff there is no such line, while Rainsford feels it isn't hunting when you deal with humans. Zaroff sees certain humans, namely sailors, as less honorable as some fine beasts he has hunted. Rainsford shares the common belief that the life of a man is always worth more than that of an animal. Zaroff tries to show Rainsford how is beliefs are reactionary and hipocritical, but Rainsford doesn't buy it.
Oh most definitely this is irony. While Rainsford's character gets caught in the irony of understanding what the hunted feels like he is unwitting until this moment. Zaroff, however, has made a concious choice despite all of his education and cultivation. His comment is ironic because he is truly evil and barbaric. Most definitely not civilized.
This is such delicious irony. Zaroff is a man who has every appearance of being civilized: his clothes are made by the finest tailor, his wines and foods are the best, his home is furnished impeccably, he listens to opera...and so on. These, though, are only trappings (excuse the pun) of civility, and Rainsford is fooled for a while. However, the room which housed the "trophies of Zaroff's human hunting reveals his true self. In actuality, Zaroff is as uncivilized as they come. This statement is clearly dramatic irony--what he says is truth is not what we come to know as truth.
It's interesting that he says civilized, as his favorite sport is hunting human beings. However, he is very proper in his dress and living conditions, which is something Rainsford notes upon arriving at Zaroff's home. Also, Zaroff has a strange sense of fairness; while it's obviously not fair at all to force a person into playing a game where their life is as stake, especially against their will, Zaroff thinks that letting Rainsford have a single weapon and a head start is enough to consider the game "fair". Civilized, it would seem, is an extremely relative term in this story.