The ups and downs of pacing in a series

I just finished a book and went to read some of the reviews on it, wondering if anyone else felt the same about it. (Is it next year yet? Because I REALLY feel the need to know what happens!)

So naturally I go to the lower star ratings first (because they are more entertaining to read--even though this was a 5 star read for me.)

I got to one of the 3-star reviews, and they said that it just "wasn't as fast-paced as the last one." But It left me wondering WHY some people expect every book in a series to contain the same elements in the same amounts as the one(s) before it.
Life has never worked that way for me, there have been fast-paced moments and horribly slow paced moments. But as long as the slow paced moments build on the plot, character development, etc. Why is it seen as a bad thing?

You can't have a 3-10 book series as one solid fight scene ... I mean you could, but that would diminish the effect of the important fight scenes right?

Shouldn't a series be filled with ups and downs?

I think so.

The book was #5. (Where book #4 started off with another character different from the first three books--the next generation--if you will.) The second book (#5) dealt with the consequences of the previous book, and set up the situations for the next book, while developing the new villains, and growing the romantic relationship so it would make sense why the MC would risk everything to save said love interest. Not a whole lot of fight scenes, but to me, it comes across as necessary for the reader to know/learn about the series as a whole to make the most sense.

Back to my main point. Is there a reason some readers expect the exact-same-formula of action and events for each book in a series? I would love to hear your thoughts about your expectations regarding pace, throughout a series.




*Please bear in mind that I also don't agree with the need to know if it's an HEA, trigger warnings, etc. I just read a book that sounds interesting to me and whatever reaction I have to it, is the reaction I have to it.