But first... SPOILER ALERT!
I mean the first time around I had some sympathy for the guy - he was a disappointed and somewhat embittered middle aged man still trying to do his best to support his family, and then he's given this crappy cancer diagnosis. I felt bad for him. Fair to say that by the time he just lets Jesse's girlfriend, Jane, choke to death on her own vomit whilst unconscious I'd entirely lost that and felt nothing but loathing for the character (which isn't to say I didn't enjoy the show, or think he was a great character).
But what I realised on revisiting the show a couple of years later is that Walter White didn't break bad. He was bad from the very beginning. I mean look at the way he interacts with people in the early episodes of season 1: he's largely an asshole. The only thing that changes is that, initially because he's driven to, he becomes much more comfortable with manifesting his assholery overtly.