I've since finished this off and it's a really neat spin on the the franchise.
Ubisoft were pretty clever in working the restrictions of being a coloured woman into ther design of the game. You can step out of your mansion (you play as a noble woman) in one of three different guises, each of which have certain restrictions and advantages.
As a noble woman you can bribe your way into places and you can get away with a lot (short of murder). Later on you get a fantastic blow dart gun built into your parsol umbrella and this ended up being my favourite way to start trouble, poisoning guards (either by killing them or sending them into a frenzy.) But wearing a heavy hoop skirt it's impossible to jump and climb. You do become a target for cutpurses though who judge you as an easy mark if you wander down the wrong alley. And if you do something really outrageous you have to kill the witnesses to get your rep' back under control.
As a slave you can blend in a lot more as long as you don't do anything too unusual, but as you're just one of the crowd if you can escape it's pretty easy to bring your reputation visibilty rating down by removing posters. You do have access to more of the toys an assasin has but only the sort of improvised things you can hide on you as a slave like a blow pipe and a machete for cutting cane.
And as the lady assassin you can essentially fight without restriction. BUT (and I love this) you can never really lower your reputation, everyone notices the lady pirate wearing the sword! Which makes a lot of sense.
There's only really three open maps (with some caves and temples inbetween) but even though it's tiny compared to AC3 it's really focused. And the swamp really feels like a swamp with only some awkwardly placed semi invisible walls spoiling the illusion. The only thing I missed was navel battles. There is a simplified trading system involving moving lots of boats around on a map but that's as close as you get to the water.
I think a lot of people are probably going to skip this in preference to playing AC4 which is a bit of a pity. It's a nice little slice of AC goodness.