Gustave Charpentier's opera "Louise" may not be totally unsung but it is rarely produced and there has not been a new recording for many years. None of the complete recordings is entirely satisfactory. However, a really splendid DVD of a 2007 Paris production is available. The sound and picture are excellent as this was a television broadcast; it's not just somebody sitting with a camera in the stalls. It's also very well sung and conducted. It's an answer to a prayer!
http://www.operapassion.com/dvd-y36.html (http://www.operapassion.com/dvd-y36.html)
I should in fairness add that the recording comes on two discs and that my copy of the second one had a serious sound/picture synchronization problem so that, in the great love duet, it sometimes appears that the voices are coming from the wrong characters! A pity but bearable.
I'd look no further than the superb set with Ileana Cotrubas and Placido Domingo...
http://www.amazon.co.uk/Charpentier-Louise-Sony-Opera-House/dp/B002DU7OMW/ref=sr_1_1?s=music&ie=UTF8&qid=1367355892&sr=1-1&keywords=charpentier+louise (http://www.amazon.co.uk/Charpentier-Louise-Sony-Opera-House/dp/B002DU7OMW/ref=sr_1_1?s=music&ie=UTF8&qid=1367355892&sr=1-1&keywords=charpentier+louise)
...btw, I'd be very careful ordering from www.operapassion.com. The one set of CDs I have ordered from them came with the tracks scrambled and they refused to answer my request for a replacement. I eventually had to seek redress through PayPal. So: caveat emptor.