When you have a vocal range that is as powerful and extensive as Sharon's you don't need to use guest vocalists. They certainly don't add anything to the album, in fact to be honest their inclusion comes across as a bit of a gimmick.
People who liked The Unforgiving will probably like Hydra as well, but anyone hoping for a return to the Mother Earth type material will be disappointed.
Once again I'm having to mark the album down due to the fact that it has been compressed to within an inch of it's life. People who download all their music probably won't care, but try playing the cd on a decent music system and the instruments all converge to produce one headache inducing cacophony.
If I were being unkind I would be inclined to sum up Hydra as The Unforgiving with guest singers and even worse compression.
Which is a great shame, because the actual songs themselves are up to their usual standard of brilliance.
An album that had the potential to be fantastic has, in my opinion, been spoilt by the use of ill-suited guest vocalists and massive compression, and if it wasn't for this I would have given it 5 stars easily.