Reviews flatten the experience
I have written on how reviews can be seen as a means of augmenting the experience of consuming media. Further, reviews can deepen how you resonate with said media. That being said, the additional experiences and the intellectual scaffolding provided by this process can also be detrimental. Consider the following three points.
You are susceptible to bias
If you are reading reviews right after you have finished a movie or book, your own opinions have not had enough time to solidify/crystallize. Any review you read will bias you, even subconsciously. And this bias isn't proportionate either. 99 positive reviews will not alter your perception all that much. But a single negative review can significantly change how you see something. As I said, it's a subconscious shift, almost imperceptible. Try as you might, you cannot unsee a negative review.
Just because you give your opinions time to solidify doesn't mean you're out of the weeds yet.
Cognitive offloading
When using reviews as a tool for literary analysis to build your intellectual scaffolding, you are outsourcing all the thinking to someone else. Sure, now you have something to talk about, but you did not arrive at that conclusion on your own, did you? You did not do any of the thinking that would let you reach that point. You know something about a book or movie, but you don't know where you got it from. The term scaffolding becomes ironic here. Yes, you're using it to build up your mental model, but the scaffolding is never a part of the building, is it? It's the difference between understanding you receive and understanding you worked your way towards.
There's quite a lot to be said about how offloading the hard part of thinking is why the feeling of not having an original thought is so endemic. In the past, I have relied on reviews by other humans to build up my mental model of a movie or a book. All the time that you spend thinking about your existing knowledge base, creating the context that informs your perspective, and re-contextualizing it is important. And they are uniquely yours, in a way my understanding of the banality of evil will never be. So much has changed personally since the first time I read The Dispossessed by Ursula K LeGuin. All of the additional contextual knowledge I have built up since then makes it highly likely that my re-read will be a superior experience.
But if you only rely on external literary analysis, it leads to a shallowness of understanding, and of experience.
Reviews diminish the effect of re-reads/watches
Maybe it's something you were supposed to understand during a re-watch, you know? Maybe the clues were there all along, and you could only spot them on your second watch. But because you have read the reviews and adopted those ideas as your own, you lose the impact of everything clicking during a re-watch. This is what I mean when I use the words 'flatten' and 'shallowness'. No two experiences are the same, but if one is made comparably shallow because of the intellectual scaffolding you possess, the scaffolding turns into a shackle.
Closing words
As I wrote in the original essay, reviews can be an additive experience that aid in expanding the context surrounding the media you're consuming. But rely on them too much, and they'll take as much as they give.