I don't think Plant hates Coverdale. He was just of the opinion that Coverdale copied his style and to an extent he's correct. Coverdale has laughed the criticism off in the past though.
As for the Coverdale/Page album, I think it's a worthwhile release with some stellar tracks. Obviously it's nowhere near as good as any of the Led Zeppelin albums, but it is a decent post Led Zeppelin project for Page.
Personally I like Coverdale as a singer anyway, eveything from his work with Deep Purple, to his solo albums and of course Whitesnake, particularly the earlier stuff. Is any of it in the same class as Led Zeppelin? No, but it's decent nonetheless.