Ok, so everybody thinks that he was an awful general.
But why? I don't know that much about his life but against Spartacus he seemed to be quite effective, as far as I know. And I mean, the decimation he order must have put order among his troops as this would make them fear him and hence do what exactly he told them to do.
Also, he seemed quite good in instilling fear, I mean, he knew how to use fear in order to put order. Like when he order all the slaves to be crucified, this made a slave think twice before revolting...