I've ran 1 session of it, which seems to be more than most people in this thread.
Wonderful illustrations. Nice setting. Lots of flavorful details, but it doesn't overwhelm you or the players with big lore dumps.
The rules for family/contacts are pretty cool. Great way to weave your characters into the world, and helps encourage players to engage with NPCs and the setting.
Rules for conflicts (which includes combat, chase scenes, and even debates) are a mess. There's some neat aspects (choosing actions in advance before revealing), but also some really baffling choices that kind of ruin any sense of pacing or drama. It can kinda work as a "story generator", I guess? But as the GM, I found it very tedious, and all my players disliked it, too.
The character advancement and "failure" didn't bother anyone, although maybe it wouldn't work for a really long D&D-style campaign. I enjoy stuff like Apocalypse World and Dungeon World, so Mouse Guard's skill system wasn't a huge change. >>53787024
Is a good way to describe it. It's really more of a "story game" than a "role-playing game". Although I think it has some of the same problems as a game like FATE: it tries to mix role-playing mechanics and story-telling mechanics, and ends up being kinda shitty at both. I'd much rather play a "pure" story game like Microscope or Fiasco.