As for book length, my feeling is that it’s up to the writer (and editor) to make the length work. I generally put down novels that feel as if they’re padded, either because the writer did a lot of research and obviously feels it must all be thrown in or because the writer has fallen in love with their deathless prose.
You see this quite often in the later novels of successful writers. Almost invariably the page count goes up and up. The poster child for this is J.K. Rowling’s Harry Potter Series. In her case I found the length was due to plot complications and multiple threads, and for the most part, it didn’t bother me. With other writers, longer length often feels like padding. Sometimes I suspect that the poor editors feel they can’t trim out excess if a very successful author’s novels — we’re talking top of the bestseller lists here — are obviously increasing in length without good reason. What do you think would happen if the million-selling author complained to the publisher when the editor wanted to trim huge swathes of prose? The editor at best would be told to back off.
For newbie authors, editors can — and often for good reason — prune brutally.
In the best of all possible worlds, it would all work out for the best. As a reader, though, I will either skip over parts of novels that feel self-indulgent in the prose, or I’ll just give up and toss them across the room.
On the other hand, we’ve all no doubt read novels that feel as if something important has been left on the cutting room floor.
It’s a fine line to walk.