Hellgate: London is an amazing game with the old concept of demons taking over the world. It seems almost like a wierd merge of a number of popular games of its time... Almost as if its developers had taken the very best of the best games, and blended it together in the hopes of a great outcome.
Hellgate: London is definitely worth playing, even if the "quests" and dialogue leaves something to be desired. Its your typical run-of-the-mill action 'rpg', with hack'n'slash components.
To really call it an rpg is a bit of a misnomer, however: the player can alter their appearance before starting a playthrough, and can add points to their various stats (similar to Diablo II), beyond that, one must rely on special gear to increase ones stats, and choose from a number of abilities in what looks suspiciously like a "talent tree": but that is the extent of the 'rpg' part of the game.
The player is offered no choices in how to deal with other people, or the demons, beyond blowing them to tiny little demon bits.
All that said, Hellgate: London is worth playing, both for its music and graphics, and I can definitely recommend playing it, if you find yourself in the mood for mindless violence.
Truth be told, however, I believe the game peaks in its opening cinematic sequence...