I would have cast it a little bit differently.
I didn't like Jason Isaacs as Michael. He is Jewish from Liverpool, for gods sake. Under no stretch of the imagination is he Irish. He could have been Moe but I am sure its not a role big enough for him.
The actor playing Moe was too good looking and clean cut to be a scuzzy psycho hit man. He could have been Michael.
I do love the series, though