Super fun, great story and animation, love the combat (especially the tentacles). Gruesome, macabre, and hilarious, it's a great buy and you won't t regret the experience.
You don't really need to play the first game, although plot and character-wise doing so will give you a deeper insight into Jackie as well as the source of his powers. Furthermore, for those of familiar with the first game, the change on abilities of the Darkness arms is welcome and incredibly fun, with some fantastic dismemberment combos becoming available. The leveling up of abilities is also pretty top and not too restricted, so you can really follow whatever play style you prefer the most or try out a little of everything.
As a warning it is a pretty gruesome experience, so not for the kiddies or faint of heart - ripping people in half or tearing off their limbs isn't really family friendly... unless you're in Jackie's line of business.