If you love every book put into your hands, you'll never need to write one yourself, I suspect. But if you're able to say, "this could be much better," perhaps there's a place for you at a desk with a laptop and a blank word processing document.
For a long time I wasn't comfortable saying what I thought about something others thought was great; who was I to rain down dissatisfaction, me from a small town, trained up in a public school system, exposed to little of the wider world or dangerous eddies of thought? It took me years to realize I had been early caught and trapped in the nice-person veneer they slap onto kids brought up in the lapsed Lutheran tradition. Be polite, don't argue, play a musical instrument in school (it's good for you), and "do good work."
I spent a long time extracting the long, sturdy thread strangling my mind that made it hard to be honest, even savage. I suspect there's a good chunk of my academic career I spent questing after books that I was told I had to like. Now I can admit that I found my last reading of Middlemarch, probably my eighth pass through, tedious.
My tastes have changed the more I'm exposed to things not quite fit to be on university syllabi. My degree of precision identifying why I don't like a given book, plot, or character has also sharpened. For instance, I had a hard time making it through the vast flabby center of All the King's Men, the section where the narrator of the tale goes into the details of his unfinished dissertation. I realized there were two books crammed between one set of covers, but only one of them was worth reading at all, the energetic rise and fall of Willie Stark. I was at peace with my harsh judgment, even eager to be so sure of what I thought. Had I been that book's editor it would have found itself embarked on a radical diet plan, slimming down by 150 tedious pages, kicking, slobbering, and pleading. (Since reading the book, I've read other commentators who have some of the same problems, but most of them don't wish for a scalpel to resolve the issue.)
It took a while to get comfortable with being mean when I read something someone has slaved over; being rude about not liking a character or a plot. I have a better idea what I like, what I'd like to read, and what I might be best at when turning to craft my own tale. Perhaps my deepest affection is for revenge tales, purpose-driven plots with inevitable complications that, at their best, should grip the reader and bloat up a thin idea into something ponderous and wonderful. They're hard to pull off well on the page or the screen as, at their mediocre average, they are often too predictable, too cardboard static. That's one reason I thought I loved the Count of the Monte Cristo, the vast anthem for justice denied and justice clawed back. But when I sat down and read it again two years ago, I found I recognized little in the story as compared to how it lived in my memory. I remembered the taut, beautiful beginning: a ship arrives, Dantes chatters about being sent on a mission to the exiled Napoleon, those jealous of him begin to plot with the available known facts, and a prosecutor afraid of what Dantes might know sends him to prison without the benefit of a trial. Even the oddness of the prison scenes and the chatty Abbe who spends years learning up the otherwise ignorant Dantes plucked some smiles out of me. Then it all went to hell, confusion, and perdition. I found myself saying "what" an awful lot through the last three-quarters of the tale. Bizarre coincidences, long-winded digressions, oddities popping up left and right: but the worst was how long Dantes took to get the slightest bit of vengeance, but not a bit of it for himself, not for the conspiracy that sent him to the Chateau d'Iff. He chose to expose subsequent crimes only, wild murder tales, mercenaries who butchered and betrayed, and things even more untethered from the beautiful opening pages which were worthy of a much better body and ending.
That's where I started my current project: writing a taut beautiful beginning of a revenge tale and then making a body that was worthy of it, digging into the people involved, keeping the cast as small as the core of Monte Cristo, putting a purpose back into something that even Dumas allowed to lose its way. As I get closer to completion, I keep in my mind that others will read my tale (cross my fingers) and try to figure out what makes them unhappy or mean or dissatisfied about it. And I look forward to that day.