I've beaten XIII twice, so I know it well. I don't hate it, but I don't love it either. My main criticism of XIII is it suffers from a lack of sense of place. It feels like a disjointed series of unconnected environments, and there's no sense of a cohesive world that you're exploring and learning about.
Lightning is on a train. Where does it come from? Where does it go to? We'll never know. Now we're in a crystal ice cavern. Now we're in a dense forest. Now we're inside an airship. Now we're at an amusement park. There is no sense of how these places relate to one another or how they're connected, and that dramatically impacted how engaged I was with the story.
The battle and hunt systems were the more enjoyable parts. The worldbuilding was lackluster bordering on non-existent. I also really dislike... actually, the whole cast. I don't think there's a single character I like. I dislike Sazh the least, if I had to choose.
But I still finished it. Twice. XV was the only main series game that I disliked to the extent that I didn't see it through.
To each their own. I know a lot of people were disappointed by XVI, and again, I could criticize a number of aspects of it. But overall, I've had more fun than I've had with an FF game since X.
To be clear, I'm enjoying XVI, and XV was the one game I disliked so much I dropped it. But try either one! Different people may like different games, and that's fine.
As far as XVI goes, my main gripes are that combat is pretty slow until you've unlocked three sets of abilities, and it relies just a little bit too heavily on its Game of Thrones inspiration. But once combat gets going, it feels really good. You can dodge or parry almost every attack in the game, and it feels pretty badass to get right in the enemy's face and have them not be able to touch you because you've learned the moveset.