It's also a show that respects its audience and its own history. Minor characters reappear at surprising times and dialogue often references past seasons. It gives the show a necessary realism at odds with the crazy things that unfold each episode.
Most importantly, though, Weeds manages to be both the most suspenseful series on TV and the funniest. That's a hard line to straddle, and all of my favorite series do so brilliantly. But none has done so consistently for five seasons. I hope we get even more. The writers' creativity could carry these characters in so many directions yet.
As I mentioned before, the fifth season premiered a few weeks ago on Showtime. If you've never given Weeds a try before, rent the previous seasons. Each can easily be watched in one sitting. It's just that good. (Plus, Mary Louise-Parker is the best thing ever)