About the negative reviews, I've seen some common things on most of them : it's hard to find a review with strong arguments, they often talk all along about Morten, though he left nearly 10 years ago and Tristania had released 3 others albums before Rubicon. For some reviewers it's like a game to bash everything they did after his leaving.
I see the word commercial used in it but I don't think changing the style of the singer with the risk to lose a part of the fanbase is something more commercial than keeping a singer in the same style as Vibeke and playing the same style with the same sound.
I agree some people can dislike the voice of Mariangela, but they still talking of Vibeke as the soul of the band and as far as I know she never was a songwriter, sometimes I wonder if they really listened the album.
There's one thing for sure in positive reviews : they listened the album. Positive reviews surely don't mean you'll like it because after all it's just a matter of personal tastes.
I don't know for the other people here but that's my opinion.
And from someone who have seen the band with Vibeke than with Mariangela, I really enjoyed more the current line-up on stage.
Welcome here anyway