So we played this over the weekend, and it is rock solid. The setup is significantly more complicated than you could expect from an indie game, but the details fall into their places as you go through character generation. The characters are based on class-like templates, which you customise as you fill out the character sheet, leaving you with a fairly straightforward dice pool system when you are done.
Gameplay is mostly based on individual heists connected by strategic interludes where you manage your guild. The bane of infiltration missions, overlong planning is reduced in very efficient ways; the characters are assumed to have discussed the risks and prepared for contingencies, and they can bring these up retroactively during play.
Interestingly, it is a game where only the players roll, and there doesn't seem to be traditional NPC stats - it is the successful or failed actions of the party which affect the severity of the opposition and the complications that get introduced into your heist schemes. Say, a character rolling badly while staking out a target would attract the attentions of the locals, making it necessary to either deal with the new risk or accept its impact on the way the story goes. The GM can also offer up "devil's bargains" to improve your success levels for tradeoffs like "okay, you can kill him, but it will raise a lot of noise, making a team of neighbours arrive within 15 minutes". Nonetheless, while this is a game heavy on collective narration, the GM still runs the scenario with a mixture of prepared elements, details emerging through play, and player input. Also, characters quickly build up stress, which eventually leads to traumatic consequences (this is the system's equivalent of a dual Hp system - and you can take off the edge of stress by indulging in your vices).
What makes the play experience particularly interesting is setting up actions and determining the oucomes - there are a lot of ways to accomplish mission goals from subterfuge to naked violence; either individually or through a robust collective action mechanic (which feels a lot like the criminals' assault of the office complex in Fritz Lang's M). Things also flow rather differently depending on the current threat level - "controlled" actions go smoothly, "risky" actions tend to end up with a lot of "you succeeded, but..." outcomes, and acting under "desperate" circumstances will mostly get you into deep shit. If you keep failing, you can attempt to do things in more risky ways, but in the end, it may end up costing you. It is a surprisingly tight simulation of Thief and Dishonored's play dynamic.
We did not dip too deeply into the downtime rules, but you can build up your own thieves' guild (or other organisation in the final game), increase your hold over territory, add special features to your hideout, improve or ruin your relations with other factions, and gain or reduce heat with the law. This is mostly tracked on a collective character sheet, and doesn't take away too much time from the heists.
All in all, BitD is somewhere halfway between traditional RPGs and storygames, and plays very well if you don't mind this kind of thing. If the GM knows the rules (and he has to), a four-hour session is enough for character generation and two medium-length heists. It is very easy to play it as a one-shot, but seems to lend itself well to campaign play as well.