It’s called a climax for a reason.
There are a wide range of emotions that overwhelm you as you're finishing a book.

Disney / StudioCanal / Via gifbay.com
Sometimes, you just feel okay.

Not every book has to be great. There's nothing too bad about consistently "okay" books.
Giphy / Via giphy.com
Sometimes it's pretty good.

It got you thinking and feeling, but you still felt a little bit unsatisfied; things could've been better.
BBC / Via amythegloriouspond.tumblr.com
And sometimes the book just sucks.

FOX / Via reddit.com

19 Reasons Why Finishing A Book Is Basically Orgasmic