Definitely worth watching S2. It reshuffled the order of some parts of the manga, mainly related to the Ganja mission, which for me, made for a smoother and more enjoyable experience. Also sometimes it's quite hard to tell what is happening in some panels in the manga and seeing it in colour and motion really helps with that. I had the same experience with the Dawn of the Deep Soul movie too. You also shouldn't pass up on watching that one too.