I feel that this is two sides of the same coin - as authors, we are always both our biggest fans and our harshest critics.
On one hand, if you as an author don't thoroughly enjoy your story, then why are you even writing? You should be writing exactly what you enjoy - anything else is complete nonsense. Think about this for a moment. If an author tailors their story to a particular audience, and writes tropes that are popular, but sacrifice their own enjoyment for the sake of viewership, then how on earth could the story actually be good?
If the author doesn't enjoy the story, it's very unlikely that anyone else will either. It's this simple. Sure, there could be some strange people out there who get a kick out of it, but you can't make something good unless you yourself like it. Similarly, as authors we take inspiration from the stories that we ourselves enjoy. I do this all the time, introducing concepts, themes, writing tactics, and mechanics that are inspired from stories that I found to be excellent. Why learn from something that you thought was bad, when you could learn from something you thought was good?
In other words, you should be your biggest fan. You should write exactly the types of stories you enjoy. You know why? Because there are other people out there who enjoy those same stories. Yes, the genres might not be as widespread or common as some of the big hitters, but in the first place - you're a small writer. You shouldn't aim to have some mainstream series, you should aim to create a hidden gem that a few people witness but absolutely love. Or at least, that is my opinion on the matter.
Now, with that being said, we are also our own harshest critics. There are multiple aspects to this.
Of course, as writers, we improve over time. We gain experience, we learn things, we try things, we fail at things. And through these failures, we learn lessons. We also learn through consistent writing and practice. And so, how often do we look back at older chapters and say to ourselves "I can't believe I worded this like that! This sounds so dumb!". And you know what - that's GREAT. If you as a writer look back at your previous writing and think 'this sucks', then it means you've improved significantly.
But aside from the natural flow of experience and progress, we can also be over critical of our own writing simply from the perspective we have of it. As writers, we don't see things the same way a reader would. A reader will only read the story once. Everything to them will be fresh and new, from chapter to chapter. But as a writer, we spend hours upon hours thinking up all the different ways in which things can be done. And then beyond that, we spend so much time writing and editing, and we end up knowing the story in and out, left and right, up and down.
It isn't much of a twist when you're the person who wrote the twist, after all.
For this reason, sometimes it can be hard to tell exactly how much of an impact the writing has on the viewers, but that's why we need to think from their perspective, and consider what is being revealed and how as a part of our writing process. I've been experimenting with this quite a bit recently, especially with writing scenes and hiding certain things only to reveal them later.
One of the best ways to experience our own writing in the way a reader would is to read it long after you've written in, once you've forgotten what has happened and don't really recall. That way, you can somewhat experience it as a first time reader, and let me tell you this is a lot of fun.
Even so, it's fine to be critical on yourself, and it's also fine to love your writing. Just make sure to balance the two. Don't be so overly critical that you become discouraged, but also don't be so overconfident that you fail to improve or see the flaws.