I've read a cool interpretation of Walt that's apparently completely false but works well. As he learns to act in the selfish manner he's denied his entire life, his decision to get into the drug game tends to have severe negative consequences for everyone he's ever come in contact. Spoilers for the first two seasons to come.
Couple all that with Walt's winning personality, and he'd make a tip-top villain. In many ways, he's the bad guy in his story.
If Walt never got into the drug game, Hank wouldn't have gone looking for him and ending up having crippling PTSD from the shootout with Tuco. If Walt never got into the drug game, Jesse's buddy would still be alive. If Walt never got into the drug game, Jesse never would have got kicked out of his aunt's house and met Jane. And we all the consequences of that. Not to mention the damage done to the White marriage and those poor plan passengers whose accident was a result of Jane's distraught father (who was distraught because of events Walt set in motion).