I thought Russell Crowe's singing voice was dreadful. Compare it to Hugh Jackman who has experience of singing on stage and this is even more noticable.
That's why I said for the most part. Jackman, Barks and Hathaway are all theatre trained and Seyfried is opera trained - they're all singers. Crowe has apparently done some theatre, but he is the one who sounds noticeably bad in the trailers (leaving aside Helena Bonham Carter and Sacha Baron Cohen who are the comedy characters anyway).
I'm bracing myself for Stars to be very much below-par, and have heard Bring Him Home is love-it-or-hate-it, but I Dreamed a Dream and On My Own should make up for it.