When Tarja Turunen joined the band Nightwish, they changed their sound because her powerful singing overpowered the band. When she has left and they replaced her with Anette Olzon, who doesn't have nearly as powerful a voice. Anette, who is probably a perfectly lovely singer otherwise, is overpowered by Nightwish, and they didn't change their sound again to adapt to their lead singer. Meanwhile, Tarja is out recording on her own, and the back-up band she's found does not do her justice, so she overpowers them. Neither Tarja nor Nightwish are really worth listening to anymore.
This concludes my whining as a disgruntled fan.