I was unable to get tickets for performances at the Paris Opera but easily got tickets at the Chatelet. The theatre program's musical theatre but also presents dance and music especially during spring and summer. Best seats probably front of circles of balcony. Front 7 rows a little flat and forward boxes would have restricted viewing. Plenty of variety of prices for tickets. At interval make sure you go out to one of the reception rooms or balcony with view over Paris.
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