I don't think they're that bad - well ok, I don't like the guitarist (thankfully he left) and the guy who sang on Bring Me Back to Life totally massacred it whereas as the version with just her is better. I think she has a great voice, I wont deny it and I wouldn't mind having strong vocals like that myself. I've listened to Fallen, Origin and all of their demos, they have some good songs but it really just gets too bland after a while and there is no variation with her singing style either. Other then that, I too really dislike her attitude regarding the music and towards other female singers in the industry. In that sense she reminds me of Avril when she first came out.
As for the Christina Scabbia comment, as much as I love Lacuna Coil, have all their albums and have seen them live... she has a great voice but doesn't really use it to it's potential imo. It becomes monotonous and doesn't progress in dexterity or power - it can also seem really emotionless and robotic, I honestly think she could do alot more with it. But either way I prefer Lacuna Coil's music ability so much more - Evanescence have yet to learn how to play real metal and move away from the limited mu-metal chords.