I don't like;
The constant, repetitive announcements for revenue producing activities. The big problem is that when they do the announcements, it cuts off the sound on the cabin TV, so when I am trying to catch up on the news, I get interrupted by the announcement for the "inch of gold" sale (again)
The bingo game right before the big show in the main show lounge. I can't make it from dinner in time to get anything vaguely resembling a decent seat because everyone is in the lounge playing bingo.
The cruise director who acts like we are all at a summer camp for 12 year olds. I hated that sthick back when I was 12, and my impressions haven't improved as I age.
The red/white/blue contest. As Shakespere wrote in McBeath, "it it a tale, told by a madman, full of sound and fury, signifying nothing."
Overall, I do like Carnival, though. After all, if I didn't like Carnival, I wouldn't book them for my honeymoon cruise.
P.S. As for the one who wanted trays in the buffet, they had trays on my last two cruises (Carnival Valor and Carnival Pride).