A high school chemistry teacher (Walt), who is both brilliant and underpaid, finds out he has terminal lung cancer. He has a pregnant wife and a disabled son and not nearly enough insurance to pay for everything. To make money to pay off the medical bills, house, and his family's future, he turns to making crystal meth temporarily. However, he invents an extremely good type of meth which becomes insanely popular. Big-time dealers get involved, and there's this revolving cast of nasty, dangerous characters. Walt gets deeper and deeper, changing along the way in ways he dislikes immensely.
The third season just started. The first season was only something like six episodes; the second was thirteen. Yes, they are definitely worth watching, but start at the beginning.