I dislike the new publishing rules that every book must be between 200 pages. It's too short for me. I grew up on classics where 500+ is the norm... and whenever I find a modern book that has more than 400 pages, I'm super happy and start reading it right away.
I'm currently going through The Vicomte de Bragelonne by Alexandre Dumas, that is around 2,000 pages long. One of the best reads I've had in a while.
I've also enjoyed immensely βehemoth by Peter Watts. It's at around 600 pages, and it needed all those pages to tell the whole story. And it was kind of annoying that the publishers made him split the last book of the trilogy into two 300 page books.
Otherland series, where the books are around 700-800 pages each, are also one of my favourites.
Anything less and I feel disappointed, unless it's a trilogy or more, as the book feels too short for me, and the story is either too rushed and underdeveloped.