I like to dabble in reviews from time to time myself and this was a great read.
One thing that I notice a lot of would be reviewers doing is confusing reviewing with reporting or summarizing. This of course occurs most with reviews based on stories, in comics, books, movies or games. I hate starting into a review to find out it’s just a poorly written plot recap, filled with spoilers to boot!
I feel that people who attempt to also create in the field they review have a different outlook and can hopefully avoid being a jerk in reviews. I always think of a scene from Daredevil on Netflix. Young Matt Murdock calls one of his father’s boxing opponents a bum and is scolded for it, being told that any man who steps into that ring deserves respect. I feel the same about most creative endeavors and approach my reviews & opinions in that manner!
There are a lot of times when people write without purpose, simply to espouse a position or convey that they have some information. Reviews have a very particular purpose. I'm not anti-spoiler, but I am in favor of meaningful reviews. Having a summary can be interesting, but it's not the purpose of a review and is only appropriate in certain contexts.
The real thing about reviewing and not being a jerk is to just take a step back and think about being conscious about what the point is. There are occasionally things that deserve heavy criticism because they're not meeting the standards that they claim to meet (e.g. all those early access video games that advertised features that were coming in a release planned for several years out without clarifying the current state of development), but that's a rare exception and that's when you have a duty to the audience to warn them that the product isn't meeting standards.
The Murdock lesson is probably one of the best ones that you can learn. You can be respectfully harsh. I've seen people really take things behind the shed and unload on them, and sometimes that's justified and sometimes that's not. There are a lot of reviewers, especially those who make videos, who go for a flamboyant over-the-top style (Zero Punctuation seems to be an early example of this trend), and many of these are fantastic.
However, a lot of imitators forget that the point of a review is not just beating something up, but rather making clear what its strengths and weaknesses are. If someone's always hyper-critical, but they're fair, their review can still lead me to buying a product because I know what is wrong with it and it may be things that don't bother me. If someone just rants and complains, that's a red flag.