How does Percy feel about Mr. D?

Percy did not like Mr. D at all. In fact, he was a little afraid of the camp director. In Percy's opinion, Mr. D lacked empathy and warmth. 
During their interactions, Percy discovered that Mr. D was actually Dionysus, the god of wine. He also discovered that Mr. D's father was Zeus and that Mr. D was at Camp Half-Blood because he had angered Zeus. Mr. D told Percy that he was banished to the camp after taking a wood nymph for a lover. Apparently, the wood nymph was considered "off-limits" to a god like Dionysus.
Although Mr. D intimidated Percy, the latter came to learn that the fearsome god had a few good qualities. For example, Mr. D caused fruit-bearing trees to bear fruit prolifically. At Camp Half-Blood, the strawberry plants always provided a good crop, enough to export to New York restaurants and Mount Olympus. Percy learned from Chiron that the money earned from the exports allowed the school to pay for its expenses.
Even though Percy did not especially like Mr. D, he learned to appreciate the value of the god's presence at Camp Half-Blood.