I listened to the "new" Nightwish and I must say that Anette has a lovely voice but NO!! I can't stand her...I might as well listen to Within Tempation and cut my wrists....
But I found that by the time Once came out Tarja had kinda lost her operatic quality, nothing like the amazingness of her voice from Oceanborn to Century Child. Not to say that her singing was bad, she just didn't sound as operatic as before. That's why Once is one of my least favorite albums...on the other hand, just when Nightwish had finally thrown away their awful synth-keyboard bridges that sounded like the casino levels from Sonic the Hedgehog (like in the cringeworthy songs Crownless and Stargazers, auiuuuugh!! and that's only to name a few) and replaced it with decent orchestral pieces, Tarja's vocal quality declined. So I think everything just started growing and happening at a bad time...
As for Anette, I can't see her ever performing epics like Beauty of the Beast or Sleeping Sun. In fact, I hope she never sings them at all. Everything that Nightwish was took a hairpin turn after the making of Once and Tarja's departure. If she had stayed on they would have been even better.Unfortunately she just had to go all diva on everyone. *sigh*
That's just my opinion. if you disagree, please don't kill me.