To be honest, even though I think maybe he was intended to be tragic to most of the readers/viewers, at least initially, but as far as my personal feelings are concerned, I would say that the only thing to differentiate him from other scumbags in the story is his bigger hypocrisy: not only does he switch from apparently honest person to a criminal in a moment, but doesn't seem to have any internal struggle at all, as if making such a change was completely normal. If he was a "villain" from the beginning and had never known any better life, it would be less difficult to somehow "sympathize" with him, or at least to judge him less harshly.

Don't get me wrong: I really appreciate "The Godfather" as a good book and good movies, the characters are well done, it's interesting to follow the story etc, but the main characters don't make me feel any sympathy, quite the opposite.