An Antihero, according to the dictionary, is a protagonist who lacks traditional heroic qualities, such as idealism or courage. While uncontroversially applied to Swearengen, Draper and, of course, Soprano, whether it fits Walter White (or whether he is a hero or villian) is a matter of vicious dispute.
As it is, of course, far from unusual that the bad-ass anti-hero has a fan club, it is the vigor of the haters that is unparalleled (literally desperately hoping WW's innocent CP son is killed to punish him). For them, there is disappointment in the ending, the perverse identification of psycopathic Todd with #TeamWalt, the longstanding, odd, demand that Walt recognize himself as they see him, followed by desperation to take Walt's ambiguous "admission" as an expression of unvarnished Truth. In part, this reflects a convert's zeal -- we all started out on #TeamWalt -- but it would also seem that he is more dangerous, seductive, than his parallels.
Or, what comes to mind is "Subversive": The Mr Chips into Scarface arc; The show's writing belying its creators' insistence that they condemn Walt -- as if they were afraid to acknowledge their allegiances openly. There is honesty in the confession scene -- Walter admits, despite appearances (and, well, how its all turned out), he feels great and that breaking bad gave him life. Re-reading early episodes reminds us of the degree to which he wasn't only performing when he snarled "You never believed in me!"
We are also reminded of the degree to which Walt is explicitly portrayed as re-masculating himself -- in the finale, at long last, he is allowed to die like a man. Rather than any modern sort of machismo (through it all, Walt basically stays sexually faithful to Skyler), it [ironically] almost feels classically heroic: He struggles for recognition; He eschews redemption, or second chances, instead accepting (embracing?) consquences; He evolves from belief in a scientific indeterminism (uncertainty?) to accepting Fate. And, of course, the settling of accounts -- leaving closure to Skyler and Marie, life to Jesse and an inheritance for Walt Jr. The last scene in the lab may have been less Gollum with Precious than Achilles with his Shield and Spear (or, maybe, Steve Jobs with his Macintosh). While it is impossible to write about Breaking Bad without acknowledging that Walt was, himself, a cancer, it's also worth mentioning Gilligan's suggestion that Walt became "irredeemable" the moment he refused to accept charity.