If you aren't watching it, what's wrong with you? Geez. Watch it tonight! Or, if perhaps you have a life and don't play The Sims and watch TV on a Friday night like some people (DON'T JUDGE ME!), DVR it or watch it on hulu. But, if you can, start in season 1. It's so well written, but damn if it isn't hella complex and confusing at times (Not like "Lost" confusing where everything just fell apart the last two seasons, but confusing because it's just so deep and detail-filled that it's easy to miss something important).
Trust me, pure awesomeness. I cannot emphasize this enough: it is the most well-written and the most underappreciated show on TV right now. Get on board people!