I never watched it when it was on TV, although a few people had told me it was good. I did try to watch an episode but never really got what was happening.
I recently borrowed the 1st series dvd, which I ended up watching over a 3 day period and ended up a bit of a zombie with lack of sleep.
It's one of those that you end up saying to yourself "I'll just put on the next episode to see what happens", before you know it your changing the dvd over to watch the next 4 episodes.