The Last Hero revolves around Cohen and the Silver Horde as they undertake one last quest to return fire to the gods (i.e. blow up the place). Racing against time to try and stop them is Ankh-Morpork (Lord Vetinari was asked to help), which means we get to see the Watch (or rather, Captain Carrot and a cameo from Sir Vimes) and the Unseen University (with Rincewind) work together. The only thing that's missing would be Granny Weatherwax and company, although adding them would be rather implausible.
I'm sure that there are a bunch of themes in the story (there usually is), but what stood out for me was the parody of the quest. There were some interesting questions raised, such as "how does someone make an accurate map to a place where no one has come back alive from?". Which just suggests that quests were made up so someone could have fun. Suddenly, I see 'trolls' in the epics.
Plus, in the book, we get to see Carrot, Leonard of Quirm and Rincewind team up (as usual, Rincewind was forced into it). It's a very amusing combination because of their vastly different perspectives - Leonard is the dreamy genius, Rincewind is focused only on survival and Carrot is the idealist. So when they encounter something, you can be sure that you get three different perspectives.
In fact, my favourite character for this book is Leonard. He usually has a rather small role, but he's actually really suited to be a main character (Does anyone know if there is such a book?). My favourite scene comes from the end. You see, for building a spaceship, Leonard is "punished" by the gods to paint some really huge chapel with a detailed picture of the world in 20 years - a task that is thought to be impossible. So, as soon as they reach home,
"Leonard began the penance for his hubris. This was much approved of by the Ankh-Morpork Priesthood. It was definitely the sort of thing to encourage piety.
Lord Vetinari was therefore surprised when he received an urgent message three weeks after the events recounted, and forced his way through the mob to the Temple of Small Gods.
'What's going on?' he demanded of the priests peering around the door.
'This is... blasphemy!' said Hughnon Ridcully.
'Why? What has he painted?'
'It's not what he's painted, my lord. What he's painted is... is amazing. And he's finished it!' "