It's been a while since I tried playing it (it was a Christmas gift long years back) but...
So in theory it's supposed to be a story generator that takes a fortune and uses it to guide story beats. But for example, I counted 11 different factors that can modify an individual fortune test, including at least 2 different sorts of metacurrency, and those modifications to the roll can happen in 3 different ways, none of which really added interesting choices or tactics to the play. The heart of the system is this elaborate conflict resolver that plays out like rock-paper-scissors-lizard-Spock only the choices aren't actually symmetrical. The "attack" option either directly trumps or at best ties every other option so there aren't a lot of tactical choices because there is pretty much always this one best thing to do (especially in terms of your character whose weapon strongly will favor doing that one thing). Further, the roshambo system itself is yet another piled on layer of randomness because all they do is modify the fortune test and they are laid blind so its not even a planning situation really. There is an almost completely hard baked in assumption that no more and no less than 3 mice are involved in any given challenge (each one laying one of the three actions that turn, while opponents lay all three at once) which means your tied to this bizarre unnecessary and unhelpful conflict resolution method regardless of the situation and have to kludge around it or ignore it.
When you are reading it, once you get your head around it, you're like, "This is going to be cool." but in practice it just isn't. It's boring most of the time and your moves feel a combination of both forced and random.
Outside of the conflict resolution system you still have this fiddly randomness which is written like the probabilities of success or failure don't matter as much as the elegance of the system. It's got one of those 'coin flip' systems where you are supposed to accumulate a certain number of successes out of a pool of coins, and they typically obfuscate away the actual chances of success (further obscured by the mountains of modifiers). The result is neither granularity of control nor any intuition about how hard any give test actually is. I suspect even the author would be stunned to see the tables of odds in the system.
It was just a mess. The system was actively getting in the way of creating a story or narrating a conflict. I kept feeling the need to ignore the system and make fiat rulings that went against the rules just for the sake of coherence.
One of the biggest clues I should have picked up on is that the examples of play aren't real examples of play, but scenes from the comics where the dice have been carefully chosen to match the story, which of course makes for a story and the expectation that the system will generate story, but using actual random fortunes doesn't really.
Beyond that, it's not really that clear that it's a setting that lends itself to RPG play. I suspect the setting is incoherent at a demographic level because there is a fundamental assumption that mouse society is basically the same as human society only the people are mice. But this doesn't really make sense outside of the narrow focus of the stories and well in an RPG you tend to have broader focus than that if you carry on a game for any length of time. You start asking questions like, "How long do mice live?", "How many siblings should a mouse have?", "Are non-mice basically animals or is everything basically sentient and capable of having a conversation?", "Just how does mouse society actually function?", "How many mice are their really?" Mice explicitly seem to have human sized families and live as long as humans, but at the same time they aren't top order predators and seem to die by the thousands. How does that work? It doesn't; don't think about it.
It's not really a spoiler that if you look at the mouse map you realize the mouse territories are centered around the upper peninsula of Michigan, which explains the epic treks required to get between mouse towns, but I don't think you are supposed to think too hard about why mouse society is structured this way or how many mice really should be in a medieval mouse empire of that size - "points of light" or not. I mean it's one of those settings that was never meant to be world building, so trying to do world building in it just doesn't work - and this comes from a guy who tries to game in the Star Wars universe.