I didn't see series 1 but I have all of series 2 downloaded.
Should I watch it or hunt down series 1 first?
Oh my. You're in for a treat. We've just finished series 2. The characters are extremely complex (Saga, especially, who has to be about my favourite character of all time -- quite fancy her too, but that's not the ultimate reason), and their relationships are brilliant too. Add in plots that unravel in unexpected ways, and stunning aesthetics, which all makes this about as good as telly gets for me.
In terms of your question, it's not essential, but given what I've just said, you may as well start with series 1. Enjoy.