My take on people writing reviews of books in a series they haven't read the previous books of: I think it's possible to do and do well for some readers with some books, but if you start reading a book and you're lost, congratulations, you have encountered the limit of that.

I used to read books out of order all the time because I bought them at a used book store and if I had to limit myself only to starting a new series if I could find the first book, I'd have been out of luck.

But doing that requires a willingness to make inferences, adjust assumptions as you go, and just generally roll with it. If I'd assumed that stuff that didn't make sense to me was a problem with the book I'd have been out of luck, too.

I think in most cases a reviewer who is familiar with the series will do a better job, but there are useful questions a fresh reviewer can answer, like "Is this a good jumping-on point?" and "Do I need to have read all the other books first?"

TL;DR - if you're trying to review book 2 cold and you find yourself lost and unengaged by the material, that's the time to be humble and admit you're not the right reviewer for this material.