Beliefs: In BW, the players explicitly write 3 beliefs for their character. These beliefs change through play, and characters get rewarded for fulfilling beliefs. At first, I thought this mechanic was a godsend - it made it easy as a GM to create situations that would easily motivate characters (besides gold, ale, and XP). And it was good at first, especially as the players started getting into the "artha" economy (artha is what characters get for playing in accordance with beliefs, and it helps them do stuff in the game). BUT the beliefs also led to what seemed like an early demise of the game to me. The characters' beliefs ultimately drove them to turning on each other because they all wanted the Tome of Architecture for different reasons. There were other lesser issues (like whether to negotiate with or kill the dwarven king) that drove intraparty conflict as well. It could've been just the way we wrote the beliefs, but the system just didn't support cooperative play to the extent I would've liked. The belief mechanic is a BIG party of BW, and while it's innovative and is well aimed at making the game character-driven, I'm not sure it allowed for enough flexibility when the rubber hit the road.
Everyday Task Resolution: This was my favorite part about BW - the way we constructed and resolved most die rolls that didn't involve combat. In short, players create dice pools. They get dice from various qualitative categories, like traits (e.g. cold blooded killer). As a GM, I would react to these rolls accordingly. If Pat tried to intimidate someone and had a cold blooded killer die in his pool, I could have the NPC react accordingly. Because we had so many wacky traits, we often found the characters in interesting situations...completely based on who the characters were. All in all, I think this worked a lot better to make the game character driven than the belief mechanic, which was too heavy handed. The major problem we ran into here was the players' desire to bulk up their die pools with dice from too many categories, which sometimes bordered on the ridiculous. I could've definitely been firmer with my GM veto power on this front.
Fighting: It's hard to envision the fight mechanic here if you haven't read it, but players script their combat actions in advance, compare moves against each other on a matrix, and then resolve. I think we all didn't like the fighting. Sometimes, it was very cinematic. But we're all rpg veterans, and the fights were really slow. Way too slow. And combat got increasingly difficult with more participants. I've cruised the BW forums, and there're lots of posts to this effect. The designers seem to roll with combat fine and can handle zillions of people in a combat. But it just didn't work for us. There was a great unintended result of this, however - because we shied away from combat, we played physically threatening scenes out until the last moment before we went into combat. So, we ended up with some really interesting and cinematic scenes, like one player being stretched between a starving dwarven mob and the pc's hanging out of the second floor of a dwarven building. In future games with combat systems I like better, I need to remember this - don't rush into combat rounds, because interesting stuff can happen in that grey zone between normal play and combat. That's the stuff movies are made of.
Social Combat: BW has a system for social combat that's like regular combat but (thankfully) simpler. We had 1 great social combat scene (the first time the pc's met 3 dwarven leaders who were plagued by infighting about how to deal with the siege of the Wastes), and a couple scenes that were meh. I'm not sure exactly what made 1 scene hum while the others didn't. Maybe Pat will have some insight on this.
The Endgame and the Leadup: I love when characters have their own agendas. But in BW, as things progressed, fissures in the party got wider and wider. One player eventually broke off from the group, and it made the game much more difficult to GM and frankly less fun to play. Though, I do understand he was trying to play in character. At the end of the game, the pc's all turned on each other, and it was ugly. As a GM, I had plenty of ammo to escalate the situation and put the characters in a very difficult position where there would've been more incentives to work together. But the party imploded. I think this is largely due to the belief system and the lack of cohesion of characters' beliefs. So, in the end, the game was kinda anticlimactic. This also happened in the demo we played at GenCon. All in all, this reinforces for me that beliefs are too blunt and direct a tool for making a game tick. (A better tool may just be looking at the character sheets as the GM and creating situations that match up well with the various traits the players have chosen.)
My Own GMing: I think I was really up and down in this game. I thought I had some great moments like the social combat with the dwarven leaders - I imparted necessary background info, gave the players a lay of the land of the 3 major factions, and kept the fun alive. I was also good in that grey zone between combat and regular play - there were a couple scenes where I thought I effectively kept the pc's in danger while keeping things moving and interesting. But the game sure bogged down at some points, especially when I gave them a chance a respite from danger. As a player, I always try to keep the heat on other players, and I think I need to do this more as a GM - I need to be more relentless. I also think I need to exercise a firmer hand when players argue for mechanical bonuses. But what I really need is practice. I've read a lot of this indie game stuff, and I drink the kool aid with some of it (e.g. creating situations for pc's instead of forcing them through a plot, trying to focus on character). But this open ended type of play is really tough, especially when trying to get on top of mechanics I don't know so well and when trying to keep everybody around the table engaged.
BW is a great and honestly innovative vehicle for enabling character-based play, but I think it's too heavy handed in the end. I like it - it pushed my game and I'd try it again. But I'd really like to wait for a rulebook that's more organized. It's impossible to find anything in there.