I think the main issue with this show that has been made abundantly clear following season 3 is that Jimmy simply isn't bad enough to be Saul Goodman. Saul, at least as he appears in BB, is totally without scruple. He cheats, he lies, he steals, and his sole motivation appears to be making money. In fact, he's a pretty one-dimensional character - at one point he even hits on his fat secretary, as if the writers wanted to show what a total degenerate he is. In BCS, Jimmy certainly enjoys the occasional con, but he's always careful to reel in his bad behavior before he seriously hurts people - as evidenced by pretty much all of season 3 episode 10.
In BB, Walter White went from 'good' to 'bad' rather quickly, but his transition was believable because there were indications that he was about to snap. He was harboring some serious animosity towards his former business partners and generally had never accepted his lot in life as a passionless chemistry teacher with a disabled son. He was emasculated by his social standing, and the cancer diagnosis gave him the courage to attempt to get even with fate.
Towards the end of the episode, Chuck tells Jimmy that all he does is break things and hurt other people. But this is beginning to sound like a mantra that the writers want the viewer to accept without critical thought. The mostly boring flashbacks in past seasons with Jimmy's former partner in crime don't even tell us that Jimmy is fundamentally flawed. Kim isn't repelled by Jimmy's antics and even takes part in one of his scams.
The whole show is failing right now, because it's forcing the viewer to accept things that he knows deep down just aren't so. Vince Gilligan is still a great writer, but I just don't think his heart is in this. Saul was a memorable character in Breaking Bad, but that doesn't mean he needed his own origin series. A far more interesting character was Mike, but I'm guessing the actor's old age precluded a standalone series focusing on him.