Three years of meetings means you probably spent more time talking about the book than actually reading it. That's a lot of hours invested for one story. I wonder if the club will keep meeting now that the big goal is done. Finishing something that long could make regular books feel too short.
Totally get the post-book slump thing. My group did a year on one dense classic and normal novels felt like pamphlets for months. Honestly makes you question the whole club format after a marathon like that.