At his introduction, Riva he says that he is deaf due to a genetic mutation similar to the House of Hanover "all of whom had hemophilia". Actually hemophilia showed up first in Queen Victoria's son Leopold, almost 200 years after the origination of the House of Hanover in 1636, and two of her daughters (Alice and Beatrice) were known carriers of the gene but it appears to have not affected any of her other seven children. However, the subsequent marriages and lineages from Leopold, Alice, and Beatrice carried it throughout the royal families of Europe and Russia giving it the nickname "The Royal Disease". It is considered one of the great mysteries of royalty as to why Queen Victoria had the gene for hemophilia as neither her father or mother had that gene.
In the initial meeting with Riva, when Counselor Troi is telling him how beautiful his chorus sounds, you can clearly see a crewman on the left side of the screen. He is wearing khakis and a polo shirt.
The goof items below may give away important plot points.
Before Commander Riker and the others are beamed down to the planet the second time (near the end), in response to the murder of Riva's chorus, Riker and Worf set their phasers to stun and holster them; but when they materialize on the surface of the planet, their phasers are in their hands, ready to fire.
After Riva's chorus is murdered, Riva goes to the Briefing Room and is staring out the windows, away from the doorway. When Picard and the others enter, Riva turns to the doorway, although he is deaf and wouldn't respond to the door's "whoosh". However, he only reacts to Picard when the Captain walks toward him from the side; and Riva would be able to detect movement as well as Picard's shadow from the corner of his eye.