@Tex - I'm a fan of the first but I have plenty of tolerance for eurojank games and their flaws. Given the narrative trailers I've seen, playing the first won't be vital (time has passed, factions leaders have changed, Jax has lost most of his abilities), but the ending and one important companion quest tie directly into the events of the sequel.
Just go in forewarned that the world design is dated and the lack of quest difficulty indicators unforgiving. It's a game in which you need to feel your way across the world, avoiding most creatures at first, slowly building up your skills and gear until you're powerful enough to steamroll anything. That said, in classic Pirahna Bytes' style, you can cheese or exploit some tough encounters to get your hands on fantastic gear early on (if you've got the patience).
Some spoiler-ish advice - follow the main quest from Goliet north to the Domed City ASAP for a half-decent difficulty curve and some good gear.