Adaptational Displacement: The Queen of Spades is one of Pushkin's lesser-known works, while the opera is extremely frequently performed in the former USSR and fairly often abroad, and has given root to many quotes known even to people who have never heard a single note of it.
Fan-Preferred Couple: Yes, Herman is an incredibly demanding part and he gets a lot of gorgeous music. Watching and hearing a good tenor sing it is always amazing. But most of the fans of the opera seem to agree: Liza is really stupid to choose that psychotic guy over loving and kind Prince Yeletsky.
Unintentionally Unsympathetic: Liza's behavior towards Prince Yeletsky (she barely even looks at him!) has earned her quite a few detractors among the fans. After all, it was her who accepted his proposal, and he is extremely kind with her, assuring her of his love and telling her he will respect her decision if she has changed her mind. Even if she realized she only loves Herman, she could at the very least be polite about it.