Adventures in reading: should a series character change?

I love a good series. They're my comfort food, whether on TV or on the printed page. I already know the characters, know what story to expect... When my brain needs a break, I read/watch a series.

But sometimes, a series is just... Done. And it seems that's largely up to the writer. I recently read two 'big name' mysteries, series that had been going for a while (one was on book #30!).

One book had its detective character change, as you would expect a real person to. He was no longer the outspoken, slightly unstable hero from the beginning, but he still had a bit of rebellion at his core. This detective grew up. I liked this book a lot.

Another book had two series characters, and although the mystery was good (really good, actually), the characters were completely flat. It was like the author had decided they weren't people who could change anymore. They were just there to deliver the mystery. Disappointing, to say the least.

What do you think? Should a series character change?

Is it possible for a series to be enjoyable without character change?

Have you ever read a book in one sitting?

Confession time: if a book gets too much buzz, I probably won't read it. The more it shows up on 'best of (fill in the year)' lists, the smaller the odds that the book will make my TBR pile. I guess it's my rebellious side talking. Once a book--or anything really--starts to feel like a bandwagon is waiting for me to get on, I'm out. Bandwagons are crowded, and someone always ends up elbowing you in the ribs.

But.

There was such a book last year: Wonder, a middle-grade that was on everyone's list. If it buzzed any more, it would've been a swarm of bees :-) So I avoided it...

But then two different librarians recommended it to me with such heartfelt excitement, I couldn't not read it. Because those librarians know their business, we all know this. So I picked up Wonder, and started reading it. And I finished it in one sitting.

I don't remember the last time I did that... And it wasn't like it was the perfect book--there were things I liked and didn't like, which is pretty normal--but it had me hooked. I felt a little like I was a kid again, reading the latest book waaaay past my bedtime.

Do you ever read books in one sitting? Have you ever? What was the book?