I used to really enjoy the piano bar. Now, not so much.
With a few exceptions, I don't think the musicians are as talented as I have experienced in the past. Often there are a handful of cruisers who take over all of the good seats every night and monopolize the song requests.
And while I love the international aspect of the entertainment staff on Carnival, the last time I visited a piano bar, the performer's accent was so heavy, I was having trouble understanding what he was saying/singing. He also distributed a rather limited list of songs, and apparently only wanted to take requests from that list.