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.
Alternate Character Interpretation: There is quite a substantial group of fans who hold the view that Carrot is evil and/or The Chessmaster. It helps that he is almost never the POV character - we get to hear what Vimes or Angua think about him but hardly ever see Carrot's actual thoughts.
He has also set up Vetinari Job Security several times: the most obvious is in in The Fifth Elephant when he leaves to pursue Angua and Fred Colon is left in charge, the watch falls apart. Not surprising given that it's Fred Colon, but Vetinari lampshades that as everyone knows Vimes and Carrot will be back soon, no criminals take advantage of the Watch’s self destruction for fear of their wrath. The book ends with Carrot very politely bullying the collapsed watch back into shape by reminding them they swore an oath to the king to do their duty.
When Vetinari has trouble reading your motives, says things like, "You drive a hard bargain, Captain," and you reply, "I wasn’t aware I was driving a bargain at all, sir," and live you have to be The Chessmaster, albeit probably a benevolent one.
Despite Vimes' almost suicidal urge to be normal in a World Full Of Crazy, he often does things that fall under Refuge in Audacity, such as arresting the military leaders of both Ankh-Morpork and Klatch under charges of Behaviour Likely To Cause A Breach Of The Peace in Jingo.
AE Pessimal. Attacking a troll, of all things, with your teeth is pretty insane, especially when you remember trolls are living rocks.
Pretty much any scene where the Feegles cut loose.
Granny Weatherwax started out as a supporting character in Equal Rites, but basically took over the book from the real protagonist by sheer force of awesome and ended up being the focus of the rest of the books set in Lancre.
Same with Vimes and the main Unseen University faculty (Ridcully, Ponder and the Librarian) taking over the Watch series (originally meant to be centered on Carrot) and the Rincewind series.
Also counts as a Genius Bonus in many cases. Only the most widely traveled of readers will get most of them, let alone some of the more obscure ones....
Genius Bonus: Everywhere. From the fake Latin, to obscure historical and cultural references...
Pratchett uses a lot of physics knowhow, especially with regard to the magic system. For instance, wizards have to deal with conservation of energy when translocating objects, and teleportation requires some very complex calculations. And the blue light that comes off Death's scythe, said to be atoms from the air being split? That really happens. It's called Cherenkov radiation.
Ankh-Morpork's awful cuisine, which is referenced particularly in The Fifth Elephant and Thief of Time, is based on two things: firstly, the pop-culture perception of British food being awful and/or British people making awful chefs, and secondly the very real lineage Britain has of low-quality food and ineffective quality control laws. Think the description of Ankh-Morpork chocolate in Thief of Time is awful? In the real world, underhanded British chocolate companies have tried since the earliest times to swindle customers by cutting their cocoa powder and hot chocolate with things like brick dust and red lead.
Makepeace Thomas Bounder, a cabbage-obsessed, potato-hating poet of awful skill featured in the Almanak, is a round-about Joseph Gwyer, a potato-obsessed poet who was so awful that he was described as the McGonagall of Penge.
Iron Woobie: Despite being the perpetual Buttmonkey, Verence always tries to do his job: be a fool and advisor to his king; an enlightened king to his people; and a husband to Magrat.
Magrat herself has a lot of this, as does Agnes Nitt.
"I wonder... am I really a bastard or am I just really good at thinking like one?"
Marty Stu: Carrot is something of a parody of this, with lampshade hanging by other characters who have trouble believing someone so perfect can be real. More specifically, he's royalty, and has all the tropes of the Royal Hero coming from humble beginnings behind him... except he just wants to be a watchman.
Stoic Woobie: Without a doubt, Death is the best person for his job, but it clearly takes its toll on him at times, most obviously when he has to collect the souls of his apprentice Mort and daughter Ysabell, at the end of their lifespans.