These are what we call the 'YMMV items.' Things that some people find in this work. We call them 'your mileage might vary' because not everyone sees these things in the same way. This starts discussions in the trope lists, a thing we don't want. Please use the discussion page if you'd like to discuss any of these items.
All in all, you could say that Fiona is a Deconstruction to the Purity Sue architype. After all, her Common Mary Sue Traits have served to be detrimental throughout the story, with the exception of befriending Hewie as without him, she would have never gotten out of the castle alive.
Squick: Lorenzo's voice. Those weird sucking noises!
That One Boss: Every boss in the game has to be defeated in a specific manner and it's easy if you know what you're doing. But if you want to get items before you defeat them, things get difficult. But the best example is the last chase with Lorenzo's burning corpse and the damn statue! The part is so hard that the players believe the statue is the real final boss.