I stay away from shows that have a loser main character.
But to call Walter White a loser is to dismiss who he is and his motivations behind what he does.
The show is a character study, mostly of Walter White, but also the people around him and the effects his decisions have on them whether they know what's happening or not. It's fascinating.
Is he always a villain? If not, when did he cross over? Did he always do it for himself or did he start off genuinely trying to care for his family by any means necessary? Did his really bad actions always have legitimate reasons behind them or was he a sadist? If not, did he become a sadist and if so when?
I've seen people who have obviously never seen the show claim it tries to celebrate drug dealing/making/selling, etc. Nothing could be further from the truth. The show attempts to turn "Mr. Chips into Scarface" as its creator put it, and "Breaking Bad" does an amazing job at it.