If they got a normal singer they would be a great rock band, but with Justin they sound more like a novelty act to me.
Great rock bands are bands like UFO and The Scorpions. For newer rock, bands like Wolfmother or Priestess. They strike me as what modern rock should be like and i have a feeling without Justin that The Darkness could probably fulfill that.
Clearly the success has gone to their heads (or Justin's at least) and has lead to bad things, they have only done 2 albums and have already mucked up.
I don't hate them, i want them to do well, but with Justin they have been more like a one hit wonder.