I loved FFXIII when it came out. It has my favorite soundtrack in the series, outstanding graphics even now, and a story that grew on me as it went along, though it did have a rocky start. The biggest draw for me was the combat and combat-related gameplay, though. Everything about it hit just right, from the ATB mechanics to the stagger system to the crystarium. I couldn't put it down for the week it took to finish, and a few days after finishing, I picked it back up for another week to do all the postgame stuff and get the platinum trophy.
I replayed it a few years later with a more casual attitude, and didn't like it as much. Losing fights became an annoyance rather than a welcome change in a series and genre that is usually not that challenging anymore. Having to keep switching paradigms to maintain buffs and debuffs and chains was more work than I wanted to put into the game. I finished the main game again, with good memories making up the difference in enjoyment (and I was still enjoying the game, just not as much as before), but didn't want to do the postgame.
So I think FFXIII is a game that gives back what you put into it. A common criticism of it from its detractors is that it's too reliant on autobattle and AI party members, which is not something I've ever seen a fan of the game say, and I guess I am such a fan, because it doesn't match my experience with it at all; if anything, it's too reliant on player input to make a good chill out game, which most FF games do. Even the story demands active engagement, with some important details only conveyed through datalog entries you have to choose to read. That being the case, it's just as well it doesn't make itself even more demanding by including a lot of exploration and hidden items and such.
I still like the game a lot conceptually, and hope to be in the right mood to play it properly again someday.