impaling!
Using the shadows, Jackie can summon a number of demon tentacles from his back. After a time, you gain more powers, fight bad guys, cross into the demon world (why? not so sure) then finally face Uncle Paulie's minions and himself.
OK, more summary than I wanted. Needless to say, this is actually quite a fun (and pretty long, if you do all the side missions) game. Some of the most fun I had was to use the demon arm, a sharp, stabbing tentacle, to impale enemies and toss them into the air. Ah, impaling enemies. There's also an impossibly overpowered black hole ability, which simply sucks any unlucky bastage off their feet and around in the air for a while, apparently scaring them to death. Use, recharge, rinse, repeat.
Jackie is dark, moody and has no redeeming values whatsoever. Go forth, my child, and kill. The plot leaves a bit to be desired – standard revenge story, really – but it's enough to justify all the killing. And did I mention there's a lot of killing?