I don't think the issue is that anyone thinks he's bad, he's a fantastic technical singer, but his voice is very "samey" on all of these Slash songs. It grates on you pretty quickly, and turns what is probably a great song underneath into a very average song.
That said, the original songs he did with Slash, Starlight and Back From Cali are very listenable to me, it's just this latest stuff which as you've just said, isn't my cup of tea. Wouldn't stop me going to see them live though.