Hard to say.
I became addicted to series because it's not as long as a movie and it was easier to fit in our timeschedule.
So we could watch 6 episodes in a row for instance

I really love breaking bad..really... But come on: 8episodes and now we have to wait a whole year for the last 8 ones?

Really??? Maximum frustration here.
Mad men, still at the top of my list for so many reasons.
The 2 first seasons of The Misfits (You got to love that Rapture song they used).
Weeds had some good moments (especially when Andy blew all his money in arcade machines).
Then the Big Bang Theory for a good nerdy laugh and Modern Family for a good "I've been there" laugh.
The one that restarted my addiction for tv series a long time ago was 6 Feet Under. It's just so dense and rich + it really has a definitive and very moving ending (but you really have to watch the whole show to fully enjoy it).
I also like Curb Your Enthusiasm but that's because I was a Seinfeld addict and I just adore watching Larry David sinking into conflicts and problems.
Damn there are so many good shows...