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.
Crosses the Line Twice: Veola makes a ring for Klein, unsubtly naming it the "Ring of Love." When Lita objects, Veola provides a new recipe "for Lita," which turns out to be poisonous pills she calls "Farewell, Love" - a note of pitch-black humor, already uncomfortable and which becomes much Harsher in Hindsight when you learn Lita actually once did want to kill herself, and Veola is planning to kill herself too. After Lita and Veola finally start to bond, Veola provides a new recipe for medicine that restores Lita's degenerating mana.
Veola: "This time, 'feel a lot better' didn't imply dying in your sleep."
Difficulty Spike: Avenberry. The dungeon is very long and enemies are tough. If you go unprepared you might not make to the next save point.
Disappointing Last Level: Selk's Cry and Mull's Castle. Short and fairly linear for a final dungeon with no memorable moments either.
Ensemble Darkhorse: Veola, a shopkeeper in the first town you visit ends up having the fullest story of all the characters featured in the game. And she isn't even a playable character.
Her story is so complete and robust, in fact (with multiple supporting cast members and almost as much content as the "proper" game), that there are quite a few theories about this game beginning life as "Atelier Veola" in the vein of its predecessors, with Veola as the player character and Klein and Lita as supporting characters. In an attempt to drive up sales (and produce something that could be exported to the US), however, Gust decided to retool the game into something a bit more "standard", and so promoted Klein and Lita to main characters, shuffled the old content off to the side, and produced what we have today - or so the theory goes. Either way, it produced possibly the finest Ensemble Darkhorse in franchise history (with only one real contender from the Japanese-only games) - a lot of people don't play the game for Klein, they play it for Veola.
She even got an special drama CD for herself, featuring characters from Atelier Iris 1 and 2. The disc was titled, yup, Atelier Veola - The Alchemist of Regalzine -. Sadly, it was a very rare Gust Shop-only preorder item, so No Export for You.
Narm: Most of the characters are so earnest that when something dramatic happens, it makes the characterization funny. Especially true of Klein, who sounds almost like his lips are pursed in angst whenever he meets adversity.
Surprise Difficulty: The game has very scarce and ineffective healing, and specially reviving, items aside from the ones Klein can learn to make. Combine that with some tough bosses, and even enemies, who can bring him down in a couple of turns and the game can get unnervingly difficult.
That One Boss: Elder Virium and Prism are both regarded to be extremely difficult bosses as they can wipe out your entire party in a matter of turns if you are not careful. Ironically, they are the last two boss battles in which the Crutch Character Arlin can be used in the main story.
From the Bonus Dungeon, the three golden pigs.
That One Attack: Elder Virum's Tera Flame, deal very high damage to all characters and it has a nasty surprise of not being a two turns move like Flickering Flame.
Prism's Shutrel Edge, although it takes two turns, it's very hard to Skill Break it; it deals massive damage to all characters and Prism may act again essentially finishing off the job.
Quetzacoatl's Towznetskarz, it may Poison and Curse (disables HP recover) all characters. Hope it didn't affect Klein.
Amalgam's Ether Light, it might Poison, Curse, Paralyze and put everyone to Sleep. Yup.