In fact I was sufficiently interested that I played it again, and the answer was “too easy”.
The whole game took roughly 90 minutes, which was a victory in straight sets, including the reset time in between the runs, and the time spent pandering to my cat who regularly wanted to lie all over the cards (and who has just flattened this laptop screen against the table, and is lying half on top of it : )
Of note, the middle run genuinely took only ~15 minutes, so I guess there’s something to the time on the box after all.
I think that gives me my conclusion, though. Once I’d figured out my basic strategy, there just weren’t many interesting decisions to make; and unless I still have the rules wrong and am now making things too easy (but I don’t think that’s the case), the game simply doesn’t hold enough challenge. So… into the ‘sell’ pile it goes.
Edit: From perusing BGG, a better method of actually increasing difficulty seems to be reducing the number of cards in the Strength and/or Hope piles. That would certainly make failure more likely, but I don’t think it would affect the decision making very much.