Yes — the trilogy must be read in order. Each book directly continues from the previous. Major spoilers stack from Book 1 through Book 3.
Yes — significantly. Book 1 is a tense but relatively light mystery. Book 3 contains graphic violence and psychological intensity. Content warnings apply. Most readers find the tonal shift jarring but ultimately worth it.
The 2024 BBC/Netflix series starring Emma Myers as Pip is widely considered a faithful, well-cast adaptation of Book 1. It covers the first novel across five episodes and introduced the series to a massive new audience.