This is a great question. General Zaroff's personality is complex.
On the one hand, he was an intelligent and cultured man. He spoke well, could be courteous, and knew how to show hospitality. For example, he read Rainsford's books, treated him to a nice meal, and was a good conversationalist. Here is what the text says:
He was finding the general a most thoughtful and affable host, a true cosmopolite. But there was one small trait of .the general's that made Rainsford uncomfortable. Whenever he looked up from his plate he found the general studying him, appraising him narrowly.
On the other hand, Zaroff had a twisted desire. He no longer wanted to hunt animals but humans. When Zaroff stated this to Rainsford, he did so with a smile. This alone shows that he was mad in the worst sense.
The general smiled the quiet smile of one who has faced an obstacle and surmounted it with success. "I had to invent a new animal to hunt," he said.
Zaroff later even said that hunting men gave him pleasure!
Finally, when Rainsford surprised him at the end by going after him, he congratulated him and conceded defeat.
The general sucked in his breath and smiled. "I congratulate you," he said. "You have won the game."
In conclusion, the general was a deeply disturbed man with some culture.