I agree with what most people said, that Daniel Day-Lewis's character really wasn't very likeable. He sang quite well I guess.
I liked Marion Cotillard and was surprised by her performance. She didn't look very comfortable being sexy, but I think that was the point.
Penelope Cruz was another surprise I thought with her voice - and so bendy!!!
Judi Dench who I don't normally like, was very good I thought. Looked very cute with that bob.
Fergie was very good. Did she put on weight specifically for that role??
Kate HuRABon was better than expected, but then her Mum can dance and sing, so she obviously inherited some of her gifts.
Sophia Loren didn't really sing her song at all, but I think she carried it off just about.
Nicole Kidman was good when she was acting, but her voice wasn't strong enough for the song she sang - I've heard much better versions of it live (and I'm sure her voice went through an Autotuner). I heard Catherine Zeta-Jones was up for the role, and I think she would've been a better choice.
I think the problem in the casting is that they went for too many 'names,' and it worked with Fergie, Kate, Judi, Marion and Penny. Obviously they needed a star for the main role, and again he wasn't too bad, but the script didn't make you like him, nor did his portrayal. For the roles of mother and muse though, you would think they could have gone for non-names as they already had enough and then the music would not really have come in for criticism - which surely is the main thing they should be trying to do with a Musical (let's not mention Mamma Mia).
There wasn't really enough plot for my liking between the songs, and they should've just released all the songs individually, as basically they were all just music videos stringed together with some Oscar-winning actors talking between them.