Here's a story on the American Idol Motown recordings, available at iTunes.
I only have and only have heard Adam Lambert's song, "Tracks of My Tears." So I can't judge the others. But I see the author of that column distributes grades from A to D, with an A for Anoop and D's for Megan and Scott.
The different thing about these recordings is that they used the original Motown backing tracks. I don't think that was a good idea, because it'd be good to refresh them at bit. At least that's my criticism of the Adam track. It sounds like it could use an updated arrangement for his massively good vocals, jazz it up a bit.
I like his singing -- rock solid -- but think he's being held back too much by the backing track that's like a straitjacket. (It also sounds, on my Ipod, like there's some small amount of distortion on this recording.)