You basically have it, Skoll. But you can be seen by the npc's(guards, vendors, cameras, etc) as long as you aren't doing something criminial(weapon out, killing someone, whatever:)
There are different play modes, some involve getting new targets and going until all but one person is whacked, some involve a new round 90-seconds after the first target is killed. After you are killed, you come back to life with a new name and identity(random) and you go about getting ready for the next round(your inventory carry over from round to round, as do your name and appearance if you don't die)
You have money to buy things or bribe npc's, you get money for killing people(more money for the randomly picked "hot" weapons, to increase variety) Most money at the end of a game(multiple rounds, usually to a target $ cap) wins. Lose money for breaking the law. Great setting and theme, very immersive into that time period, with period music and dress. Their website with more info and graphics is at www.theshiponline.com so you can get a better idea, but I'm liking it.