Septimus Heap/YMMV

Angst? What Angst?: Septimus seems pretty unconcerned for the disappearance of Nicko in Physik.
Awesome Art: Mark Zug's drawing s of the characters and settings in the books.
Bellisario's Maxim: Applied by Word of God to many aspects of the setting.
Canon Fodder: Numerous details, places and people across the series.
Complete Monster: Queen Etheldredda the Awful. It is strongly implied that she drowned her children (except Esmeralda, who escaped, and Marcellus, who was needed to make the Immortality potion) so that she could be Queen forever.
Continuity Lock Out: If you haven't read Magyk before Flyte or Physik before Queste, you won't understand much of the plot.
Ending Fatigue: The books have an habit of lasting long and even after the climax, there is usually still a bit of plot before the end.
Fan-Preferred Couple: Septimus/Jenna and Marcia/Silas in spite of the fact that Septimus and Jenna are siblings and that Silas is married and has seven kids.
First Installment Wins: If you read about Septimus Heap, chances are you will read mostly about the first book, Magyk.
Harsher in Hindsight: The events leading up to the outbreak of the Darke Domaine in Darke bear an uncanny similarity to the Fukushima accident, namely the safety lapses in both cases.
Ho Yay: Between Septimus and Wolf Boy.
Idiot Plot:
- Played With in Darke. Sure, it was Merrin Meredith who unleashed the Darke Domaine, but it probably wouldn't have happened without Septimus's and Marcia's poor safety policy.
- The escalation of the crisis was also hardly the paramount of good decision-making.
Informed Wrongness: Jenna is a MacGuffin Girl and is told to go away in Syren rather than get into danger, notwithstanding the fact that she isn't one outside of the Castle.
It Gets Better: A few people complained about the lenght of Queste's introduction, specifically the Merrin Meredith scenes.
It Was His Sled: Septimus wasn't actually dead in Magyk.
Magnificent Bastard: Tertius Fume. Between dragging Alther into the Darke Halls when he's Banished, sending Septimus on the Queste with a rigged Draw, he's definitively a magnificent antagonist, especially compared to his rather dull predecessors.
Nightmare Fuel:
- The Two-Faced ring, and the way you get it off. You have to take it off the Other way, i.e you have to cut the finger off it was on.
- The Hunter. Going around and killing people like animals. It's even called "hunting". His relentless efficiency mode.
- The illustration of a Thing in Darke.
- Some milder examples: Septimus's appearance Darke and Jenna's witchy clothing in Darke; DomDaniel melting down to a pool of slime in Flyte; Merrin Meredith being Consumed by DomDaniel in Magyk.
Nightmare Retardant: The Things' faces, as shown in Darke, look almost weird, rather than scary.
Relationship Writing Fumble: Septimus and Jenna, to the point where many readers thought they were going to be the Alpha Official Couple. The fumble is strong with this one.
Shipping. Many: Septimus/Jenna, Marcia/Milo, Marcia/Marcellus and the list goes on and on.
The Scrappy: Milo Banda is often considered an idiot for his actions in Syren, namely for always being away and a huge annoyance to Jenna.
Too Good to Last: Not all fans are pleased that there will be only 7 books.
Uncanny Valley: Septimus's illustration in Darke can be ... a little disconcerting, what with the absent-minded and distanced look.
Viewer Gender Confusion: Merrin Meredith's image.
The Woobie: Sarah Heap. Between losing Septimus, Simon and Nicko at various times and rarely seeing any of them, there is not much happiness in her life.
What an Idiot!:
- Marcia puts up Jenna for the Heaps to adopt in Magyk despite different eyecolours and Magykal powers making them a rather poor hiding place for the princess.
- What did you intend when running back into the Palace when the Darke Domaine was spreading out, Sarah?